GEN 1 pokemon RED BLUE Legality

[squirtlexxi]

Hello, everyone. I'm new here. I use PKHex for 6 months, and I'm very satisfied about it. My question is: When I edit GEN 1 Pokemon (caught in RED BLUE saves), change male or female, change their nature. Their PID  and the legality icon stays the same.  Can I trust in it, or is it better to not change gender and nature? When I do the same thing on GEN 3, 4 Pokemon they get ILEGAL. 

 

The same happens with the GEN 2 Pokemon (caught in GOLD SILVER saves) I edit gender natures and they still legal, with the plus that the encounter saying "egg", but they weren't.

 

PS: I transfered my GEN1 and 2 Pokemon, using Poke Transporter, and I'm edit them in a Ultra Sun save.

[Kaphotics]

There isn't enough met data stored in the PKM to indicate the exact encounter you obtained it from. All it has is the met level, and the moveset really.

It finds a possible encounter, checks the moveset being possible, then settles. If an egg could have originated it, or a wild slot, or a starter, what's to say it is one vs the other? An egg will more often be legal, as it is more permissive with levels AND moveset (egg moves, inheritance) compared to other encounters, hence why it is evaluated first (successfully).

As for PID correlations, those are only a thing for generations where the correlations exist. For VC transfers, the game generates a random PID and EC, and Nature is based on the experience value it is transferred with (modulo 25).