On Stackoverflow the [AS2] tag has been used for both purposes basically forever - I answered a question on the transport protocol on December 5th 2009, and there are many ActionScript version 2 questions just as old.
What is the best usage of the [AS2] tag? And in general, should tags favour usefulness over correctness? (not that I'm sure if either use is correct here)
The correct tag for ActionScript version 2 is [actionscript-2] and there is no other meaningful tag one could give the transport protocol - people who use the protocol only refer to it as AS2, never as Applicability Statement 2.
The [AS2] tag has been added as a pseudonym for [actionscript-2] (My answer on the protocol has sadly been retagged with [actionscript-2]!) which is correct in that people tagging ActionScript questions with that tag should be warned to use the accepted tag, but not so correct that it removes the usage of the tag for the protocol entirely - you can no longer search for [AS2] tagged questions and get the protocol.
Personally I think there needs to be some sort of disambiguation page, like that offered by wikipedia.
That however would be a bit of work to implement so maybe the whole thing should just be accepted as is. AS2 is a tiny subject area on Stackoverflow (like really really tiny) so my main concern is my inner taxonomist getting twitchy.
*I could have sworn I asked a similar question to this a year or so ago but can't find it here on Meta.