There are two ways a vendor can retire an API version. It can reject calls to the dead version, which is loud and annoying and gets fixed the same afternoon. Or it can keep serving those calls out of a newer version, which is polite, invisible, and much worse.
Meta does the second one. From Meta's Graph API versioning docs:
A version will no longer be usable two years after the date that the subsequent version is released.
and, immediately after:
For APIs, once a version is no longer usable, any calls made to it will be defaulted to the next oldest, usable version.
