Aye, I suppose a seige is a seige wether it lasts a year or a week, so you are right, but long scale seiges by attrition were rare if not unexistant in mesoamerica as all evidence points at. It was simply unfeasable to do anything other than simply intimidate or force the beseiged city into surrender in the opening week, with a massive force or through battles, raids, etc. prior to the seige itself, which was ultimatly always the end game.@Saxdude I can't speak of the peculiarities of meso-american warfare, but I can tell you right here and now that throughout European history, sieges have been very common and very much unavoidable, no matter their relative unpopularity. Of course no one in their right mind would want to fight a 2-years siege - but they rarely get a choice in the matter. If one side has a massive defensive advantage, it sure as hell will use it.
Plus, you have to remember that not all sieges are two year affairs. Most of the time, warfare consists of moderately defended locations switching hands, and field engagements between detachments seeking to capture or protect such.
If a city was nigh impregnable then the answer to that would be to wait for a moment in which it wasnt, cut off its allies and engage in irregular warfare until the moment for a direct assault on the city or its own voluntary submision is feasible.