My wife and I have recently gotten back into biking, resurrecting our mid-'90's vintage Specialized bikes for the task.
Both bikes have spent the last dozen years stored in our unfinished basement. It's never too cold or hot down there, there's no UV to speak of, and moisture is in the normal "basement" range.
After our first couple of rides, I replaced the Team Master on the rear of my stumpy. It was shedding side knobs at an alarming rate. The Team Control on front has suffered a few torn side knobs, but is holding up. It'll be replaced in the spring.
My wife's Hardrock AX was virtually new off the store floor, maybe 300km on it its entire life. It had the stock Hardrock'r tires on it. They've shed no lugs, but show degradation of the skinwall portion of the casing. It hasn't bulged or split in any way, but the natural rubber covering the cords is dryrotting. The tread has worn quickly, the rear I replaced last week after about 400kms this summer, the front will be replaced next year.
I'll say again, these tires were stored in a relatively protected location. They're not up to real use.
J