Alpha and bèta mean that there is lack of polish, both in visual (textures, shadows, lightning, etc.) and functional (spawnrooms, cappoints, working doors, etc.) aspect. Unknown bugs simply cannot be filled under one of those two, as the player is responsable for doing crazy stuff, like going to places where he shouldn't go. Valve fixed a ton of these bugs, but they don't qualify as a bug in my opinion. A map never reaches final as weird things can always be found if looked after.
But in terms of releasing, I don't see the point in releasing an unfinished map. But then again, there a lot of good maps that call themselves alpha, where they could easily be called final. It's not because a mapper adds of fixes things that his map was in alpha or béta stage. It's should be seen as version 1, 2, 3, ... all the way up to the last one.