Unpleasant surprises while collecting postmarks...

Today I celebrated a milestone in my decades-old pursuit of Crimean postmarks: I now have 250 Imperial-period (excluding prestamp) postmarks on file, and 252 Soviet-period (up to 1945) postmarks. And I still find new postmarks almost every week, and certainly every month.
To give you some idea of how incomplete this little database must be: I am aware of 110 post offices (of various classes, excluding town post sub-offices) that were active during the Imperial period. I have recorded postmarks of 53 of them. The Soviet period is even worse. There's a 1937 listing by Andrew Cronin that lists 273 offices, of which I've seen 75. Clearly, I have a lot more collecting to do!
However, every now and then I find out the job is even bigger than I thought.
Let's start with multiple serial letters. It's a well-known phenomenon that you can have multiple postmarks with the same serial letter for a given location. The later-Imperial double-circle postmarks are often found in a "large" and "small" version sharing the same serial letter, and of course, postmarks had to be replaced sometimes too. Even so, some places on the Crimea drive me nuts. Baidary is a good example. I have 4 double-circle postmarks in my files. ALL FOUR WITH SERIAL "a"! I mean, come on! If that multiplicity is typical, then I'll be collecting postmarks until I die.
In the Soviet period, the 1930s can be a little like that too. Most postmarks seem to exist in two versions. The older version (early 1930s) has (placename) KRYM in the top half in Cyrillic and (placename) in the bottom half in Extended Latin. The later version has KRYM (or rather, QRbM) in the bottom half as well. So for any given serial letter you are likely to find two postmarks.
But Gurzuf added insult to injury!

FINE! Two postmarks with serial "v", both in the older type. And yes, I am aware the bottom of the two has the dodgy dots that denote NKVD censorship, but still!

Now let's talk about city post sub-offices. Even during the Imperial period these just pop up like odd surprises. On the Crimea, Sevastopol', Simferopol' and Feodosiya certainly had them, because I have the postmarks, but were there any others? Dunno!

The Soviet period is even worse. Take a place like Saki, a small town on he Southwestern coast.  Why on earth did Saki, of all places, have this:

SECOND town sub-office, no less! And then this pops up from Feodosiya:

Very nice, and now I know what "gorodskoe" looks like in Crimean Tatar, but damn....

I'm going to be collecting these postmarks until I die, and I'd better be long-lived!