diff --git a/packages/rs-dpp/src/data_contract/document_type/class_methods/try_from_schema/common/mod.rs b/packages/rs-dpp/src/data_contract/document_type/class_methods/try_from_schema/common/mod.rs
index 8c75d1474dc..42e89cf3cfe 100644
--- a/packages/rs-dpp/src/data_contract/document_type/class_methods/try_from_schema/common/mod.rs
+++ b/packages/rs-dpp/src/data_contract/document_type/class_methods/try_from_schema/common/mod.rs
@@ -1525,12 +1525,13 @@ pub(super) fn parse_doctype_aggregate_keywords(
     //
     // Note on pre-v12 contracts: contracts created before v12 used the
     // generation-1 parser, which ignores these fields. After v12 upgrade,
-    // deserialization uses the generation-2 parser which will read them. This
-    // is safe because the contract update path runs through that parser with
-    // full_validation=true, and the primary key tree type is set correctly at
-    // contract creation time. Pre-v12 contracts can only have these flags if
-    // they were explicitly set in the schema — the meta-schema allows them as
-    // optional boolean properties.
+    // deserialization uses the generation-2 parser which will read them.
+    // Meta-schema v0 does not declare these fields: it admits them as unknown
+    // keys of any shape, so a pre-v12 contract carrying one was never
+    // validated against it, and reading it would assume a primary key tree
+    // type the contract was not created with. No such contract exists on
+    // mainnet or testnet; see `try_from_schema_generation_3` for the census
+    // and the rule that follows from it.
     let schema_map_opt = schema.to_map().ok();
 
     let documents_countable = schema_map_opt
@@ -1986,11 +1987,11 @@ pub(super) fn parse_index_only_keyword(schema: &Value) -> Result<bool, ProtocolE
 /// doctype-level keyword they predate (their meta-schemas still reject them
 /// under `full_validation`).
 ///
-/// Every entry must be a string. The meta-schema enforces that under full
-/// validation and a stored contract can only ever have passed it, so a
-/// non-string entry is a malformed schema on either path and is refused
+/// Every entry must be a string, on either path. A non-string entry is refused
 /// rather than silently dropped: dropping it would record a smaller set than
-/// the author declared.
+/// the author declared. A contract admitted under meta-schema v0 was never
+/// checked against this keyword; `try_from_schema_generation_3` states why the
+/// stored path is strict all the same.
 pub(super) fn parse_property_name_list_keyword(
     schema: &Value,
     name: &str,
diff --git a/packages/rs-dpp/src/data_contract/document_type/class_methods/try_from_schema/v3/meta_schema_v0_stray_keyword_tests.rs b/packages/rs-dpp/src/data_contract/document_type/class_methods/try_from_schema/v3/meta_schema_v0_stray_keyword_tests.rs
new file mode 100644
index 00000000000..833e36218bf
--- /dev/null
+++ b/packages/rs-dpp/src/data_contract/document_type/class_methods/try_from_schema/v3/meta_schema_v0_stray_keyword_tests.rs
@@ -0,0 +1,85 @@
+//! Doctype-level keyword names that are already taken by stray keys.
+//!
+//! The document meta-schema v0 admitted every contract created at protocol
+//! versions 1 to 11 and does not refuse unknown doctype-level keys, so such a
+//! contract may carry a key no validator ever looked at. The rule for reading
+//! keywords off those contracts is stated on `try_from_schema_generation_3`.
+//! What stays open is the name of a future keyword: one named after a stray
+//! key would change the meaning of the contracts that carry it, from the block
+//! that activates the keyword.
+
+use serde_json::Value as JsonValue;
+use std::fs;
+use std::path::Path;
+
+/// Every doctype-level key that no closed meta-schema declares, carried by a
+/// contract admitted under meta-schema v0. From a census of every contract
+/// create and update transition on each network (2026-09-20), decoded from the
+/// raw bytes. Mainnet: 54 admitted contract versions below height 398435,
+/// where protocol version 12 activated. Testnet: 3347 below height 362782.
+/// None of them carries a generation 3 keyword.
+///
+/// The lists are exhaustive and final. Neither network has a stray on a
+/// contract admitted later, and the set can no longer grow: every create and
+/// update since protocol version 12 is validated against a meta-schema that
+/// refuses unknown keys. So a new doctype-level keyword is safe exactly when
+/// its name is absent from these lists, and the census never needs repeating.
+const MAINNET_STRAY_DOCTYPE_KEYS: &[&str] = &["mutable"];
+const TESTNET_STRAY_DOCTYPE_KEYS: &[&str] = &[
+    "mutable",
+    "comment",
+    "position",
+    "tokenCosts",
+    "indexes",
+    "bls_public_key",
+    "keywords",
+];
+
+/// The meta-schema that leaves the doctype level open. It declares `keywords`,
+/// which no later meta-schema does, so it is not checked against the lists.
+const OPEN_DOCUMENT_META_SCHEMA_VERSION: &str = "v0";
+
+/// Pick another name, or decide what happens to the contracts that carry the
+/// stray key first.
+#[test]
+fn should_not_name_a_doctype_keyword_after_a_stray_key_of_a_meta_schema_v0_contract() {
+    let meta_schemas = Path::new(env!("CARGO_MANIFEST_DIR")).join("schema/meta_schemas/document");
+
+    let mut checked = 0;
+    for entry in fs::read_dir(&meta_schemas).expect("the document meta-schema directory exists") {
+        let directory = entry.expect("a readable directory entry").path();
+        let version = directory
+            .file_name()
+            .and_then(|name| name.to_str())
+            .expect("a meta-schema version directory name")
+            .to_owned();
+        if version == OPEN_DOCUMENT_META_SCHEMA_VERSION {
+            continue;
+        }
+
+        let source = fs::read_to_string(directory.join("document-meta.json"))
+            .unwrap_or_else(|e| panic!("document meta-schema {version} must be readable: {e}"));
+        let meta_schema: JsonValue =
+            serde_json::from_str(&source).expect("document meta-schema JSON must be valid");
+        let keywords = meta_schema["properties"]
+            .as_object()
+            .expect("the document meta-schema declares its doctype-level keywords");
+
+        for stray in MAINNET_STRAY_DOCTYPE_KEYS
+            .iter()
+            .chain(TESTNET_STRAY_DOCTYPE_KEYS)
+        {
+            assert!(
+                !keywords.contains_key(*stray),
+                "document meta-schema {version} declares `{stray}`, which contracts admitted \
+                 under meta-schema v0 already carry as a stray key"
+            );
+        }
+        checked += 1;
+    }
+
+    assert!(
+        checked >= 3,
+        "expected the closed document meta-schemas v1 to v3 at least, found {checked}"
+    );
+}
diff --git a/packages/rs-dpp/src/data_contract/document_type/class_methods/try_from_schema/v3/mod.rs b/packages/rs-dpp/src/data_contract/document_type/class_methods/try_from_schema/v3/mod.rs
index e479e4d3379..9912479a0ed 100644
--- a/packages/rs-dpp/src/data_contract/document_type/class_methods/try_from_schema/v3/mod.rs
+++ b/packages/rs-dpp/src/data_contract/document_type/class_methods/try_from_schema/v3/mod.rs
@@ -233,6 +233,40 @@ const RANKED_INDEX_KEY_LENGTH_CHECK: common::RankedIndexKeyLengthCheck =
 /// Full validation rejects keep-history document types that allow deletion.
 /// Stored contracts bypass this check so legacy contradictory schemas remain
 /// readable and can be repaired by setting `canBeDeleted: false` on update.
+///
+/// # Doctype-level keywords on contracts that predate them
+///
+/// Not every stored contract was validated against the keywords read here.
+/// The document meta-schema v0 admitted every contract created at protocol
+/// versions 1 to 11 and leaves unknown doctype-level keys open, so such a
+/// contract may carry a key named like one of these keywords, of any shape.
+/// Meta-schemas v1 and later refuse unknown doctype-level keys, and the
+/// property and index levels were closed from v0 on.
+///
+/// One rule covers every doctype-level keyword of this generation: it is read
+/// wherever it appears, and its shape is enforced on both the validating and
+/// the stored path. No keyword gets stored-path leniency.
+///
+/// * Nothing this parser receives records which meta-schema admitted the
+///   contract, so a well-formed stray cannot be told apart from a validated
+///   declaration. Leniency could therefore only ever cover the malformed
+///   case, which fails loudly, and never the well-formed one, which would
+///   silently change the meaning of a contract (for `indexOnly`, the storage
+///   layout of documents already written).
+/// * `full_validation: false` is not only the stored path. `check_tx` and
+///   client-side parsing take it too, so leniency there widens what an
+///   unvalidated schema may contain.
+/// * Refusing is the safe failure. It is deterministic across nodes, confined
+///   to the one contract (its transitions end as an internal error, which the
+///   proposer leaves out of the block, so the chain does not halt), and
+///   repairable in a later protocol version.
+///
+/// What makes the rule safe is evidence rather than code: a census of every
+/// contract admitted under meta-schema v0 on mainnet and testnet (2026-09-20)
+/// found none carrying any of these keywords, and that set closed for good
+/// when protocol version 12 activated. `meta_schema_v0_stray_keyword_tests`
+/// records the stray keys those contracts do carry, and fails if a document
+/// meta-schema ever declares one of them as a keyword.
 #[allow(clippy::too_many_arguments)]
 fn try_from_schema_generation_3(
     data_contract_id: Identifier,
@@ -247,17 +281,12 @@ fn try_from_schema_generation_3(
     validation_operations: &mut impl Extend<ProtocolValidationOperation>,
     platform_version: &PlatformVersion,
 ) -> Result<DocumentTypeV2, ProtocolError> {
-    // Read the aggregate and indexOnly keywords before the core parser
-    // consumes `schema`.
+    // Read the doctype-level keywords before the core parser consumes
+    // `schema`. Each is read wherever it appears, and its shape is enforced on
+    // both paths: see "Doctype-level keywords on contracts that predate them"
+    // above.
     let aggregates = common::parse_doctype_aggregate_keywords(&schema, name)?;
     let index_only = common::parse_index_only_keyword(&schema)?;
-    // Like every doctype-level keyword of this generation, `actionFees` is read wherever it
-    // appears and its shape is enforced on the validating and the stored path alike: no keyword
-    // is softened for a stored contract. The frozen v0 meta-schema (protocol versions 1 to 11)
-    // did not refuse unknown top-level keys, but a census of every contract create and update
-    // on mainnet and testnet (2026-09-20) found no contract it admitted carrying this key, and
-    // every create and update since is validated by a meta-schema that refuses it. So every
-    // declaration a node reads from state was validated.
     let action_fees = DocumentActionFees::try_from_document_schema(&schema, name)?;
     let immutable_fields =
         common::parse_property_name_list_keyword(&schema, name, property_names::IMMUTABLE)?;
@@ -403,6 +432,8 @@ mod index_only_tests;
 
 #[cfg(test)]
 mod keep_history_tests;
+#[cfg(test)]
+mod meta_schema_v0_stray_keyword_tests;
 
 #[cfg(test)]
 mod tests {