First of, a good read. (that reminds me to update the picture in that post)
So, every time a Pokemon enters HOME from a different game, a small subsection of HOME's data for that Pokemon is updated.
So if the pokemon never enters Legends Arceus, the Legends Arceus subsection in HOME will remain blank.
As that data is only in HOME, and not on the pk file itself, the mon would appear the same when you edit via PKHeX.