I think we mentioned this in this forum a while ago, but the fact that when ash saw piplups in a zoo in XY, he mentions that he knows a piplup with an attitude. Which can only point to ONE piplup, the one we all know and love and had as much interaction and screentime as pikachu had in that series. And this is ASH we are talking about. He forgets about HIS pokemon as well, nevermind others. The fact that he remembered and even bothered to add that comment shows how much he cares and remembers about dawn.