There’s the regulations and then there’s the regulation tests for the legality on the car. My guess is Mercedes and Honda were making their engines to the regulations, whereas Ferrari were, at least, in part, designing their engines to pass the tests so their illegality can’t be proven via normal FIA means- this is probably why a settlement was reached, FIA probably knew they were cheating the regs but cannot prove it via their standard testing methods.

I also always felt this was the approach RBR had with their flexi wings back in 2010-2013ish.