Specifics about memory mechanics from Gen 6 onward

[JLSgolden]

Hey there!

I already looked for answers to this question but coulnd't find anything satisfactory.

Question is: Say a Pokemon from Y remembers that I beat a gym leader with it in my team and later I beat the champion with that same Pokemon, will the memory always 100% in every case update to "battled on the trainers side and beat the champion"? Or is that only a percentage chance and therefore not always the case?

Is there a "memory hierarchy" so some memories that the games deems more important will always be remembered? Probably difficult to find the answer to but thought I'd give it a try.