One more caveat:
The Proffieboard tester is designed to test as many features of the proffieboard as possible. It is not designed to test all the features of the CPU itself.
I think what happens is that ST-micro makes the same chip and labels some STM32L433 and some STM32L431. Some may be labeled that way because some part of the chip doesn’t work, so it can’t do the functions of an STM32L433 chip, while other may be labelled that way just because of supply and demand reasons.
Either way, I think it’s a bit of a gamble.