Perfect Era Accuracy - A specific era of t2a perfectly replicated. This concept is obviously an ideal and can never actually be achieved.
Selective/Eclectic Era Accuracy - A different ideal which inherently contradicts Perfect Era Accuracy. Selective era accuracy would be the ideal of including different aspects of all eras of T2A. For example, having stealable house deeds *and* house lockdowns at the same time.
Social Era Accuracy - The population and demographics of the original T2A. To elaborate, one of the arguments I've seen presented for the reason the game has a different social "feel" to it, is because of the lack of "noobs". Most of the people who play UO today are the hard-core players who really got into it. Most people here have 7x GM characters, know the dynamics of pvp, know exactly what skills to raise, how to raise them, where to hunt, etc. In T2A, not a very high percentage of people were 7x GM, not many people actually knew a whole lot about the game. Social Accuracy would entail perfectly replicating said T2A demographics. Obviously, this is an ideal and can never be achieved, but may prove to be a useful term?
Economic Era Accuracy - This is most likely impossible to achieve. The goal of this would be to perfectly replicate the economy during the original T2A. This would include things like item prices and prevalence.
Technical Accuracy - This would deal with certain client-side things like era accurate third party utilities. i.e. Should Razor be allowed? Is it similar enough to UOA to be allowed? Would OSI have endorsed it like they did UOA?
Peripheral Accuracy - Small things, like the text displayed when an item is single clicked, which font to use, etc.
Mechanical Accuracy - This includes any T2A mechanic: spell damage, cast time, certain bugs, skill delays, line of sight, server lines, etc.
Political Accuracy - This would deal with any t2a policy, like the anti-macro policy that was included in the original T2A, the question of whether automated events should be allowed, how many accounts a player is allowed to have, and so on.
Byproduct Accuracy - Changes that aren't exactly accurate, but would create an accurate situation through inaccurate means. As far as I understand, byproduct accuracy would encompass things like server births and black dye tubs. They existed in t2a but were introduced pre-t2a. So the inaccurate action of adding them in game, creates an accurate situation: they exist.
The way I see it. Right now we have perfect era accuracy as a kind of general goal. Mechanical era accuracy is pursued all the way in terms of pvp and certain other things, but what about bugs? Why hasn't the hide repair bug been included, or house loot bugs? House loot bugs obviously haven't been included because they can be used maliciously. That's understandable, but this leads me to believe that perfect era accuracy is not top priority in every case, and is more of a general goal which can have exceptions. Should there be some criteria or a method by which to determine what is considered a reasonable exception?
Peripheral accuracy seems to have been pursued all the way. There's been some debate about technical era accuracy in the past. Political accuracy doesn't seem to have been pursued at all.
Byproduct era accuracy has been coming up here and there in threads lately. i.e. Should people be limited to only one account so that it's harder block house spots with ghosts? Not a strictly accurate change, but as a byproduct it creates an accurate situation. Nobody remembers anyone blocking house spots with ghosts, do they?
Another topic relating to byproduct accuracy dealt with magic weapon drop rates. An example of implementation of byproduct accuracy here would be: Having monsters drop less magic weapons because our population to magic weapon ratio is too high, even though monsters have the same drop rates here as they did in the original T2A. The change is not strictly accurate, but if the change is implemented, it creates an accurate situation as a byproduct: good magic weapons are harder to come by, like they were originally in t2a. This would end up helping economic accuracy, but it would ultimately violate mechanical accuracy by changing the magic weapon drop rates. What is more important: mechanical or economic accuracy?
I think it would be good to identify exactly which concepts of era accuracy we currently go by and evaluate which are the most important. What do you guys think?
(If anyone else has conceived of terms that may be useful in discussing era accuracy post them here.

edit: Revised a lot.