Of course, but there is still that (bulbapedia says) 1 in 4,294,967,296 chance of it happening so not impossible right? That's the biggest thing I want to understand. I do get that 99.99999% of the time it's been hacked to do it but it's not technically illegal is it? From what I thought, the legality checker is for illegal, which are impossible, things and stuff that extremely unlikely like shiny 6V gen 3 Pokemon are still legal.
Reason I ask is because I want to be seen as the original trainer for a transferred move mon so that it doesn't have the exp boost, I can change the nickname if needed, and so that people I trade the Pokemon to can see my ID and SID if they use a save editor themselves. It doesn't do much else and gamefreak allows you to battle and trade with them so it doesn't seem to affect online.