Places of note:

• Everywhere where we check FCV before verifying if a stale config exception has a shard ID
• Places where we check FCV before throwing a ShardInvalidatedForTargeting error.

Noted files (not exhaustive!):

• https://github.com/mongodb/mongo/blob/bb741a0ab1b2c80844dab55a3beecd83a8250ca4/src/mongo/db/service_entry_point_mongod.cpp#L199-L203
• https://github.com/mongodb/mongo/blob/bb741a0ab1b2c80844dab55a3beecd83a8250ca4/src/mongo/db/commands/mr.cpp#L1646-L1650
• https://github.com/mongodb/mongo/blob/bb741a0ab1b2c80844dab55a3beecd83a8250ca4/src/mongo/db/s/scoped_operation_completion_sharding_actions.cpp#L83-L87
• https://github.com/mongodb/mongo/blob/3f117d24cf8eed745b45baaf147fc33168f18170/src/mongo/s/client/parallel.cpp#L917-L920