Hi Michael
If you search the forum you may find other reports of chips having more internal resources than expected. I don't think that it is bad chip marking but more a production strategy, whereby if you need 64k you should order 64k parts and not bank on smaller ones having enough memory since that will not be guaranteed.
As reference, the well known BluePill boards (with ST Micro STM32F103) usually come with 128k Flash whereas the STM32 part on the board has officially only 64k Flash. The maker community picked up on this fact and so use the board regularly for programs requiring more than the 64k official Flash space. There are however boards with the same chip which then do not operate since they only have 64k (that operate). Search the board on Wikipedia for more details.
There is speculation about parts being manufactered with more Flash but specified with less so that Flash area failure can be accounted for and the phenomena is not restricted to any particular manufacturer, but what is true is more likely a secret. At the end of the day you can't rely on getting more than is on the package so if you do it is an interesting quirk but has no relevance to correct purchasing of the correct devices as needed by the product in hand.
Regards
Mark
