How did that happen if they were in cases?
Because they came OUT of the cases so I could gig on 'em! At the time, which was easily 15 years ago anyway, these were my main gigging set and I had no idea as to the damage UV would cause with the older pyralin pearls, WMP being probably the worst. In the summer months I play a LOT of outdoor venues, and well ... you can guess the rest. Again, you don't really SEE it happening. It sneaks up on you, and it does take time for the damage to show. Anyway, lesson learned there. So, with my 1950 WFL Buddy Rich Classic's, I NEVER gigged those outside, and there was no issue! They stayed right where they were with regard to yellowing of the WMP, and I had those for years. Today, WMP wrap is UV STABLE!, so this is no longer an issue. For a lot of guys that own vintage WMP .. ( and that's ALL I own outside of some COW and COF where applicable for BR ) .. you just don't want to subject the wrap to lots of sunlite, and/or UV in general... within reason of course. Thing for me is, I play/gig ALL my drums/sets, as that's half the joy of owning them. But now, I am better armed with information on some of the issues that "can" happen. In this case, lesson learned the hard way! 15/20 years ago though, the vintage drum collecting/hobby was a relatively "new thing", so there was a learning curve!
Tommyp