I think it's pretty well known when the size of modern comic books changed from Silver Age to modern age...(for me, it was about FF #94 or so, though I didn't notice it at the time)...
but I have another related question...
Many of the older Silver Age Marvels suffer from what is known as "Marvel Chipping"...flakes of the edge of the cover that break off, or chip away. Eventually, this fades away as the issues get newer or better paper stock.
Is there a specific date or issue numbers where we find this type of damage stops suddenly?
Or is it a case where individual issues are simply not cared for, and the yellowing and sun fade that follows as a result can fatigue and cause Marvel Chipping in any book?
Any knowledgable collectors know this one?
I can't shed any light on dates but as for "chipping", a lack of proper care can be one reason for this, e.g. not storing the comic carefully, mishandling, storing unbagged, in too dry or too moist conditions. The phenomenon isn't limited to Marvel as some Dell titles suffer this way. Mainly because as the spine rolls, the outside edge of the cover becomes more exposed and therefore more prone to damage. I've just read Roy Rogers #46, 1951 and it has "chipping".
When bagging old comics, always be careful while sliding them into bags, particularly Mylar and Mylites - they're notorious for catching tiny imperfectionson spines and outside edges and making them worse.
Also, as you mention, the paper used in old comics is poor, particularly on Charlton comics, and as such, was never designed to last. Which is another reason NM copies command much higher prices - they are simply rarer.
I have to say the problem is much, much worse with pulps.
As it happens, I have one issue of DOC SAVAGE-- the original pulp magazine. I bought it some years back at a convention, probably more as a curiosity piece than anything else. Quite a few years later, I was plowing thru several boxes of books and magazines I'd bought over the years and somehow never read, and got to this one. It was a fun read-- but I remember having to be extra-extra careful, while reading it, trying to treat it as delicately as possible, to prevent any damage. I didn't want the thing falling to pieces in my hands!
If I recall, the issues was "The Too-Wise Owl". I know it had something to do with an owl that had had its intelligence increased tremendously, but for the life of me, I can't remember what it had to do with the plot (whihc involved kidnapping and a gang of really dangerous, bloodthirsty thugs).
A number of years ago I was at a charity auction with a buddy of mine, and he won a small lot of comics. One of them was a golden age Daredevil comic and at the bottom of the bag you could see like little paper (wood) shavings there it was beat up/falling apart so bad.
I have several 60s Marvels that have some chipping. It also happened with a 1950 Archie. I don't know when it was fixed but I remember that for awhile in the 70s the printing looked cheaper and more faded even when new than the flaking 60s comics. They apparently fixed one problem only to get stuck with another a few years later. The poor printing happened right after they announced they'd finally become number one. So they celebrated beating DC by making cheaper comics?