Just a question as to how one might tell a pack has been resealed. Does the flap on the back of the pack have to be loose (edit) added photos 
I believe they reseal the packs with heat of some sort. Possibly something like a hair straightener?. I’m not sure though. If you have a pack you know is good, compare it to the one you are questioning.
My problem is that I bought the packs almost ten years ago and I’m not sure whether a pack is good or not. Some have the flap loose and some don’t. Would like to know as I’ve kept them as a part of my sealed pack collection but if they turn out to be resealed packs then I might as well open them.
if you bought them 10 years ago I wouldn’t worry so much. Pack searching wasn’t as common back then because they were not worth as much as they are today. The back flap on packs can come loose straight from a booster box. I would look at the seams on the packs for signs of tampering, but I think you’re all good. Will you post a picture?
P.s. some people will tell you otherwise, but I recommend keeping you packs sealed.
My worry wasn’t if the flap was loose but rather sealed to the top seam. I’ve uploaded pics of two packs as examples.
after looking at the pics, i think you are fine. this is common with older packs from what i understand. i have a few fossil packs like that also, where the back flap is not attached at the seams. hope this helps
My thoughts were that if the pack is attached at the seams its resealed. Since I would assume when resealing they would cause the flap to be crimped onto the seam. So loose flap is good and attached is bad?
No, packs come originally attached at the seams. From the factory. Sometimes over time the flap will become undone from the seams. Packs were not made to last a long time and be preserved.