Sorry for the late reply. I did not see your edit to your VM till just now.
In the Arceus update, unhide the Update notes. Then Find:"Checks in Order of Overall Effectiveness" - you should spot it without any problem.

First, even if its listed as a check, sorry but i dont give a fuck about it, sometimes, analysis say the worst thing and nobody check it.

Now, as I said in my post but it seems you didnt read it, there is a difference between being able to check someone, and being a check TO someone. If he was a check, he would be able to switch in, since yes, a check need to be able to come ...
The difference between a check and a counter is slim indeed, the check cant come as he want, he need to be aware of something (like a move or taking too much damage if the game is too long), a counter dont give a fuck about anything, he can and put his ass on your face.

Anyway, read this post again (= http://www.smogon.com/forums/showpos...4&postcount=37 ) if you need some explanation, i already explained what's the difference between the two.

Edit : i just read the analysis, its nowhere said that terrakion is a check, can you tell me exactly where you saw it ? Because as far as I read, they are saying what im saying to you ...

Umm.....see this: http://www.smogon.com/forums/showthread.php?t=3469167.
Terrakion is listed as the #1 check.

A check does NOT need to switch in. If I use your definition of check, then there would be a very slim difference between a check and counter. Also, yes, a revenge killer is considered as a check.

answered to your question, hope to be clear.