The HP is a full self-contained work and not a little cameo, so I am almost positive this will qualify as 1st app. NYX #3 is CGC 1st app. of X-23 for one full page panel.
There's nothing else to call it, really.
As for it selling out... yup, it's going fast.
Isn't it just one illustration, no story?
Same billing as every other work in it. There is art, there is text (Rowling's). If CGC designated "1st stories" rather than 1st apps., would give pause.
You donate to a good cause and you get a piece of history. I'm not going to obsess over the particulars...
+1
It's a cameo at best. There is not context for a story to be associated with it. You can't really compare it to many other appearances because they are part of a story.
I'm just stating that if people are only buying these to have them slabbed, you may not get what you are hoping for.
Do you have a pic of the page they appear on?