“Forever” stamps in US terms are what 1st class / 2nd class stamps have always been in the UK since they appeared in the ‘80s, where they remain valid for a level of service forever. The US went through a weird phase where they had 1st class stamps, but they would only actually be for the monetary value of whatever the 1st class rate was when issued, so if the rate went up you’d have to add extra postage.

The basic split between what has barcodes and what doesn’t it that the everyday “definitive” stamps (both 1st/2nd etc. and those with a direct monetary value) were withdrawn and reissued with barcodes, but commemorative and special stamps weren’t. Basically, stuff sold to stamp collectors to be put in a box and never used on postage doesn’t have them.