There are a couple things that i think you guys are overlooking.
1. CIK engines, chassis, and tires are homolagated for six years at a time, on a three year cycle.
2. Many chassis have remained essentially the same. For example I have a Road Rebel. My understanding is that the chassis is virtually identical to a RR fifteen years ago. The accessories have changed, for the better, but the chromolly frame is what it was then.
3. Once again, going back a while, didn’t Jordan Musser (please excuse me if I got his name wrong) come out of nowhere and win Rotax in about 2002 with a TonyKart that was mid ’90s and had been sitting for years?
There may be some exceptions. I know a TK dealer brought in karts used for one round of the world championships at sra, and there was suggestions it may have been a softer steel (ie not chromolly).
Things may also be different if you’re looking at a 30 or 28mm chassis.