STORM2K

I was wondering if any agency has ever classified a fully tropical cyclone to then classify it as "subtropical" after it already has been tropical? I've never seen the NHC do that and it's always "the cyclone is gaining extra tropical characteristics" never "the cyclone has turned into a subtropical cyclone". It's only ever the other way around. Has it ever happened or does it happen all the time and the NHC just doesn't do that?

The NHC never considers a tropical cyclone "subtropical" if it's undergoing extratropical transition (check the AOML FAQ for more on that).

RSMC La Reunion monitored a subtropical cyclone last month, and in its operational reanalysis, determined that it transitioned from a tropical depression to a subtropical storm (technically depression subtropicale - "subtropical depression", but it had 45 kt winds).