Most of my SR-25 magazines are from about 12 years old from the assault weapons ban sunset to now, including the ones LMT sold for a while. There are only maybe 10 to dozen pre assault weapons ban magazines that I have. I had access to the then banned magazines during the ban for testing, I don't recall but a few issues then, I didn't own them.
To be totally honest though, the by far large majority of my KAC magazines for these are from the introduction of the EMC line to now. I'll admit that most of my older magazines for these are not as regularly used as the newer ones. When I bought newer rifles, more magazines were purchased, and then got used with them. Older magazines got stowed away with their associated rifles and not used as much. Then I bought more rifles and magazines and so on...