>>27991773No, they reuse old dex entries all the time, and not just in remakes.
X and Y didn't have any new pokédex entries for the 649 pokémon before it. Not even for 5th gen. They usually at least have new entries for the prior generation, since they're still new.
>>27991806From what we've seen of Sun amd Moon this definitely isn't happening. I miss the superlong RSE entries and I don't understand why they've never done it again.
Just having it be new is good enough though. You can often get new details, even if it's mostly old info reworded. I want to see new entries for the gen 6 mons.