Different FWIW, issue encountered several years ago was with some older AA12 wads that had become brittle in their original packaging. The wad fingers would snap off if tested by hand. I was scoring very poorly with them even tho they 'sounded' normal. Went to the grease plate and discovered that they were apparently shattering and turning into molten plastic by the burning powder that was blown up into the shot and leaving the bbl. as a semi-solid projectile, much like the old classic 'whistler' one sometimes got from a paper hull loaded too many times w/with too many pin holes in it and everything from the brass head forward went out the bbl. usually making a whistling noise when it did so. Solution to that issue is to put any wads whose petals are brittle in the trash and do not load them.
I can corroborate that. My experience was with the WAAF114 and a Winchester Ball Powder. The wads were about 10 years old and looked and felt fine. They left melted plastic in the bore. I've used Claybuster and Remington wads twice that age with no such issues.
I don't load fiber wads as I have no application for them. This thread is however interesting.
I wonder how much the crush section or lack thereof plays a part. Seems like gas sealing might be only a part of it.
