Yeah with a layer of behind-the-scenes information you can easily get into a situation of calling everything different than what you saw or heard before a retcon. Like having Sickbay on Deck 5 onscreen in two episodes versus the TMoST book stating Deck 7 is where Sickbay is. There isn't anything onscreen that put Sickbay on Deck 7 so there isn't any retroactive continuity occurring unless you put TMoST information in and then you'd have to ask which way is retconning? Did the retcon make Sickbay always in Deck 5 or always in Deck 7?
Another area where waving retcon around that can get out of hand is not allowing for change between episodes. Ships get modified and upgraded all the time in reality so it would be somewhat unrealistic to call anything a retcon without considering that possibility.
But this informs us of your approach so yeah, good stuff
Here's a few examples of what (I think)
I know about real world, behind the scenes, creator intended retcons in TOS; the term Laser was replaced with phaser, the term lithium was replaced with dilithium, the term Engineering Deck was replaced with Engineering Section, Kirk's quarters on deck 12 were replaced with quarters located on deck 5; and there are a few others, but that's enough for now. And yes I'm aware of the many ways fans try to accommodate terms like this, and that can be fun, but that doesn't negate the fact that it was the intention of the creative staff that the new terms replace and retro actively overwrite the previous terminology.
I don't really want to get into the whole sickbay debate, because I'm still in the process of gathering facts to support my theories regarding same. But suffice it to say that I suspect that the first use of deck 5 for sickbay in
Amok Time may have been a mistake (see my previous post waay up thread) and in one sense it definitely was, because the production staff never should have pinned down the location to a specific deck and instead kept it vague, as was their usual custom for such one-of-a-kind locations. For example in
The Corbomite Maneuver Kirk leaves Sickbay and gets on a turbolift that goes up to the Bridge, but then he changes his mind and decides to stop by his quarters first, this implies that Sickbay is below Kirk's quarters which are in turn somewhere between Sickbay and the Bridge; and the original script was even more explicit with a notation that the turbolift decelerated and then began to move horizontally on it's way to it's new destination (and this is also in the Blish novelization). So
TCM script and onscreen info leave the exact deck location of Sickbay vague, as it should be, but at the same time hint at the general relationship between Sickbay, Kirk's quarters, and the Bridge.
And before I drop the subject, one more point to ponder; In
Elaan of Troyius the line about Sickbay being
"the best protected part of the ship" sounds suspiciously like -and may have been inspired by- TMoST's statement about Sickbay which says
The outer section (surrounding the central sickbay complex)
is a "protective shell" complex of water and other bulk storage”. Consider also that, in the Blish novelization, the "deck five" line in the turbolift is
missing, but the "best protected part of the ship" line is there, so if this reflects the way the script was written, then perhaps John Meredyth Lucus was aware of the info from TMoST and was attempting to use it as a reference, but then singer (perhaps?) who was tasked with revising the final script draft (Which Blish may not have had) noticed that there was no destination dialog for the turbolift and so added the deck five line, perhaps without knowing, or caring, that that he was working at cross purposes to Lucas. Of course, this is all speculation on my part, I just throw it out there as food for thought and to give some insight to the method of my madness.