They've basically dropped it.
We got a bit of info on the 16-year timeskip in the second livechat with Marco:https://www.youtube.com/watch?v=yXIhF8ezsQI
Transcript of the relevant question below:
[25:04] Q: "How was it to spend 16 years alone, and then come back to Earth as a kid?">"This is a great question. Yeah, a lot of people want to know... if... I've been deeply, deeply affected.">"And well... I can tell you that, it's kind of a weird feeling. I feel... I remember everything that happened over those 16 years... definitely... can... remember it all.">"But it... since I got back to Earth it's all becoming... a little more and more hazy. Like... almost like... a memory you had when you were a kid or something. You can remember it but... it's getting harder and harder to put details together.">"Although I do remember Nachos, my dragon cycle.">"I remember my sweet sword. I remember my abs.">"And of course... the lovely Hekapoo." (she portal smacks him again)>"You know what? Maybe I'll go visit her soon."
So he can "remember it all", but it's "getting harder and harder to put details together". He likens the experience to thinking back on "memories you had when you were a kid or something". But he can definitely remember Nachos, swords, abs, and Hekapoo.
Personally, it just feels like a cop-out answer so he can avoid answering questions about things that have never been set in stone by Nefcy/storyboarders. That's why he just pivots to listing things that we saw happen in the episode, it's just him falling back to obviously canon details. But that's just my own interpretation.