While updating some CRs in flight, I went to copy the text for the new license from an existing file and noticed a duplication of the license header (at differing levels of indentation).

I batched together a quick script to look for this pattern and it appears to be in these 36 IDL files exclusively (no .h/.cpp files from what I can see).

src/mongo/db/auth/address_restriction.idl
src/mongo/db/auth/auth_types.idl
src/mongo/db/auth/generate_action_types.py
src/mongo/db/catalog/health_log.idl
src/mongo/db/commands/end_sessions.idl
src/mongo/db/commands/list_databases.idl
src/mongo/db/commands/profile.idl
src/mongo/db/commands_test_example.idl
src/mongo/db/commands/txn_cmds.idl
src/mongo/db/commands/txn_two_phase_commit_cmds.idl
src/mongo/db/create_indexes.idl
src/mongo/db/free_mon/free_mon_commands.idl
src/mongo/db/free_mon/free_mon_protocol.idl
src/mongo/db/free_mon/free_mon_storage.idl
src/mongo/db/generic_cursor.idl
src/mongo/db/kill_sessions.idl
src/mongo/db/logical_session_cache_stats.idl
src/mongo/db/logical_session_id.idl
src/mongo/db/ops/single_write_result.idl
src/mongo/db/ops/write_ops.idl
src/mongo/db/pipeline/document_source_change_stream.idl
src/mongo/db/pipeline/document_source_list_sessions.idl
src/mongo/db/pipeline/document_source_out.idl
src/mongo/db/pipeline/exchange_spec.idl
src/mongo/db/query/tailable_mode.idl
src/mongo/db/refresh_sessions.idl
src/mongo/db/repl/apply_ops.idl
src/mongo/db/repl/dbcheck.idl
src/mongo/db/repl/oplog_entry.idl
src/mongo/db/repl/replication_consistency_markers.idl
src/mongo/db/repl/replication_types.idl
src/mongo/db/repl/rollback.idl
src/mongo/db/s/add_shard_cmd.idl
src/mongo/db/session_txn_record.idl
src/mongo/db/transaction_commit_decision.idl
src/mongo/db/transactions_stats.idl