Collecting Unused Self-Adhesive Stamps From USPS

" The adhesive has probably changed over the years as recent forever stamps are usually not soakable"

The adhesive may or may not have changed, but it has absolutely nothing to do with the soakability of the stamps. The earlier versions were soakable because the stamps were made with multiple layers and one of the middle layers was a thin layer of regular gum. After you soaked off a stamp the adhesive and a very thin layer of paper remained on the envelope paper. The change was they removed the thin layer of regular gum from the middle.

"there are issues with the acrylic adhesive "oozing" with time and without pressure applied."

While I have seen this with some European self-adhesive stamps (Denmark? I no longer remember), I have yet to see such an issue on US stamps.

One issue on US stamps I have seen is some older ones that were die cut to deeply so the die cuts cut thru the top layer of the backing and the adhesive was then able soak into the backing and it was very difficult to remove the stamps because the edges were stuck down. And some 2431 (the first self-adhesive issue when they were re-introduced in 1989) have a minor version of the adhesive migrating to the front of the stamps (the worst ones still look better than the best of the 1552), but the first mass produced ones from just 2 years later (2595-97) show no such problem.