Great info, I've never seen the "crackle effect" before but see exactly what you are talking about. Reason #7439 why I absolutely love this site.
I'd also like to add my two cents if I may.....
Much like the main reason we're all here (lol), I almost exclusively collect raw cards from this era and earlier. I am by no means an expert, and certainly cannot afford cards of this magnitude. However, I have found one tried and true test that has worked for me thus far..... (please hold your laughter.....) The good ol' fashioned smell test, literally.
I'm fairly certain every single card I own that's pre-1960-ish has a distinct smell. Like an antique book, old, kinda musty but very distinct smell. If it were a cologne it would be called "le magasin d'antiquités"
Some cards are stronger than others, but they all tend to have it. Just my personal experience and again I am by no means an expert
