Rewatching sophomore year, there's a moment in Spring Break! I Believe in You! Part 1 where Kristen revivifies herself using her own pinky bone, and Brennan says the tip of her pinky finger glows with starlight forever after. That's never acknowledged again.
I might be mistaken, but I'm pretty sure Kristen still has the staff of doubt in Junior Year. She didn't use it once in the Night Yorb fight. And Siobhan didn't once use the bonus action divination spell + dodge action from the Sword of Sight in that fight either.
Fig's birthday being christmas is based on a bit where Emily misremembered that the infaithable bass was a christmas present, said that in character to Gorthilax, then ran with it.
Brennan said it in the BTS interview: it's hard to remember all the pre-established canon. "I can't just make something up, I actually answered that 4 years ago. What did I say?"
The Quangle is almost certainly a plot-point. But it's also a de-facto explanation for all the biggest fuckups Brennan and the crew might make forgetting years of established continuity. It can be both.
AND it won't be able to explain player or GM mistakes like forgetting items, spells, abilities, relationships, lore, characters, etc. They're all friends playing a game, with various levels of obsessiveness about the details of it. Some (Ally) are pretty much just there for the vibes. I think the crew would much prefer an audience who can go with the vibes and let the show do what it's gonna do. This isn't an epic fantasy series written by one person over years where they rewrite and edit each book before publishing, making sure to reference their notes so everything is properly foreshadowed and paid off and stays consistent.
For nerds like me who WANT it to be consistent, who relish all those little details and get upset when the crew forget about them, we can write fanfic to indulge in those things. But the crew wanna keep the ball rolling uphill. They're improvisers, and they're going with the flow. Continuity is most important in improv when it hightens the bit, and when it doesn't, it usually gets dropped.