Thanks for referring to REMINDER: New Rich Text format kicks in on Oct 15th Diakoptis 
We did not catch that.
“many of which were not officially launched”
Probably we were using a feature that was never officialy supported 
So, no problem with the deprecation process here.
@Joe_Trollo thank you for the API example. Maybe having some specific “this is deprecated, see here” help message would be a great improvement as well. Did look for a http 20x HTTP response code for something like “conditionally OK”, but that doesn’t exist.
We will improve our API error handling to cope with the Asana deprecation process, which in turn would actively warn us via Sentry → Slack.