Interesting article, lots of information.

Anyway, I haven’t printed PLA for some time (years really) and recently got a few spools for free. Newest one was 3 years old, oldest 9. Out of 6 spools only one was unusable (unopened, bambulab, i believe, it turned into oily paste), two opened spools were really dusty and first layer on the spool got brittle, underneath they were fine. Oldest was verbatim and it was perfectly fine.