Not at all. There are some that exist, but I bet a good amount of the total population have been resealed
No, you're not.... It's actually a very wise approach similar to how one should rightly be cautious with supposedly original rolls.
If it is a good year it usually has a stamp on it with the year on it. If it's a plain white box, there's a 99.99% chance it's from 82-84.
I've heard there are ways to narrow it down by indicating which "lot" they came from. Cant remember specifics though. Something about the boxes or the color of the box or the labels. Maybe @blu62vette knows