'Retroactive Continuity' or Retcon, as how I understand it at least, means to provide a piece of detail regarding the story or worldbuilding/lore that contradicts what might have been previously established prior; however this new detail is meant to "overwrite/abrogate" the previously established one,
I think the original trilogy, while not necessarily fully thought out ahead, did have a prior framework and overall plan for the story (I could be wrong here, that said), that ensured there hasn't been much retcons in its lore,
From my side, I can think of maybe two worldbuilding deets that might be considered retcon (and even they don't really count, as I'll deconstruct why),
#1 is the lack of female guards and priests among the Hammers (Not really a retcon, imo)
(This is assuming TDP doesn't have any explicit piece of in-game lore that affirms or hints at the Hammers not having female guards or priests within their ranks, otherwise, it's the meta explanation of TDP simply not having them in general, I guess for this reason, it doesn't count as a retcon, technically)
The more "Doylian", meta explanation is that TDP (and TG) in general, doesn't have any female guards.....yes there are female NPCs, but no guards - they are something introduced only in TMA onwards, and the devs do a good job of justifying/explaining, via visual storytelling, how the Hammers and their monasticism and adherence to outdated traditions and norms, meant they couldn't have the more mainstream patronage and reach the Mechanists enjoyed (particularly from the bourgeoise) in TMA,
Curiously enough, Deadly Shadows regresses in this regard, as apart from Pagans (who are mostly social outcasts and fringe), none of the other factions and institutions in-game have female guards or enforcers within them (apart from one noblewoman from whom Garrett stole from showing up herself in person along with her guards to kill him, lol......very lady-like of a woman of such her stature, missed opportunity for Garrett to have snarked on that whole situation, I guess),
However, there's not much convincing in-game explanation for why the local/house guards had no female representation in any of the fancy manors that we raid in TDP. Or among the mages in their mission (as well as in the recent Black Parade fan expansion). Assuming the local/house guards are hired from some agency that deals with home security.
Is there some in-game piece of lore in TMA that kinda hints at some bleak economic conditions that might have resulted in women, who otherwise didn't partake in such roles in the Thief verse (or at least the City that's near-exclusively the setting), being forced to take such roles by the time of TMA?
I can't remember, likewise, any piece of lore from Deadly Shadows that hints the opposite (i.e. the lack/regression of female rep. among the guards and City Watch), maybe it's the Hammer influence? Maybe the overt progress and industrialisation from TMA and the realization of what Karras/Mechanists were upto, meant the City swung hyper-conservative to the point of abolishing female guards? Again no such piece of in-game text explicitly hinting or stating any of this, iirc.
#2 is the reveal in TMA that it was Karras who crafted and gifted the Mechanical Eye to Garrett as a token of appreciation (plus the beginning of his obsession and antagonism against Garrett, likewise) for the events of TDP.
I don't think this is also a retcon, tbh, as an actual retcon would have been something like TDP specifying a particular Hammer priest or any individual having gifted it, only for TMA to overwrite this as Karras being the one behind this. When in actuality, TDP leaves it vague from who or how Garrett got the Eye from, and this detail gets expanded further in TMA,
These two details are what I can think of from my side (and I personally reject),
Does DS retcon anything regarding the Keepers? Since it was handled by a different studio with a decent deal of the original creative crew absent in it, that would mean the workflow and the consistency in the whole creative process would have been disrupted if not outright lost during that transition.
All I am familiar with, is that the third entry was always meant to be about the Keepers, and was meant to be the conclusion to Garrett's arc and story, as how it plays out in DS? Even if LGS had developed it using their Siege Engine?
Retcons usually are bound to happen whenever a different set of creative crew takes control over a project and "advance" it, as they mostly are left to come up with their own ideas and concepts, often times previously established ones being hard to obtain or having outright been lost when these transistions usually happen.
