My '73 Nova had a downgrade in rated HP from 285 to 185 mostly because of going to SAE Net over "gross" HP. Ten of that is due to the added AIR pump. The rest was just a change in ratings mandated by the guvmint. The old ratings were engines on a test stand with no accessories and no exhaust.
There is a new rating which is even more precise GM uses, but the difference is minimal.
I've noted before that the GTI's small 2.0 L is rated at 220 hp, but of course it's boosted.