It's pretty normal for game assets to follow their own version of Parkinson's Law https://en.wikipedia.org/wiki/Parkinson%27s_law and expand to fill the memory / performance budget available (usually at least +5-10%). That can be just a consequence of artists and designers trying to make the best game they can within the budget available to them and so isn't particularly a bad thing. That's why an experienced programmer building in a 'secret' extra buffer for use around ship became a thing.

Yeah, I've seen something similar done to the art budgets, but hiding memory from programmers is impossible if they had any clue, especially on PS2/Xbox (32M/64M RAM). You could read .map in 5 minutes and see anything suspicious. Same with delay loops - good luck with that. Though I've observed some "miraculous" recoveries due to utter idiocy. E.g. a PS2 game using double floats (because your time calculations will break after few hours with a 32-bit float, duh!). The CPU had 0 double support so they were all done in software and the library with it was rolled into the standard math lib. Or some incredibly misguided GPU programming done to a "non-lead SKU". Nobody notices that one system runs 5 times slower than another until it's close to shipping and you try to bring it to QA.