Review the sticky shed thread. (It's a sticky...)
Avoid any *backcoated* Ampex tape that has the Ampex logo in the middle of the box. (Or the plain grey boxes, which is even older) NOS or not, It is certain to eitehr be sticky or go sticky. THat doesn't apply to *non-backcoated* tape like 631, 632, 641, 642, etc.
"Ampex" branded tape that has the logo on the bottom could go either way depending on when it was manufactured. Ampex/Quantegy switched to a new box design, about the time they changed formulas. I think the approximate date can be found in the sticky thread, but I'm pretty sure NOS after 1995 is going to be OK.