If you take care of the tractor, I dont think you would have to rebuild the engine that many times. Sure there would be wear and tear, and accidental damage, but not destructions of engine and drivetrain...
I've been thinking back, and can only think of three sleeve kits for sure, so I may have been wrong when I wrote 4. But destruction of the engine before rebuilding it? No, we didn't wait that long.
My grandfather was the second owner of the tractor, so I don't know what kind of care it had before he got it. He put in the first aftermarket kit, partly to increase the bore from 3 1/2 inches to 3 5/8, which was supposed to add 7 drawbar HP. It also switched it to aluminum pistons, and he replaced the magneto with distributor ignition. I was too young to be paying attention at the time, so I'm not sure when that happened.
My Dad put in the second kit, some time in the late 70's as I recall. I helped with that one. Rings had worn out, and every time they did those aluminum pistons wore a little more, too, making it less time before it needed new rings again. With that tractor, at the time, the cost of replacing rings, pistons, wrist pins, and bushings was such that purchasing another sleeve kit was only a little more, and there was a better chance of lasting success, so he went that way.
I put in the last one, about 9 years ago. It probably should have been done sooner, but by then there were no sleeve kits around - you had to buy individual parts from a dealer - if you could find them. But then we spotted a New-Old-Stock aftermarket kit on eBay - and snatched it up. It's still in good shape, but then we don't use the tractor quite as much as we used to, so it hasn't had as much wear.
Personally, I don't think that 3, or even 4, rebuilds in 70 years for a tractor that has spent much of its life being used for hours on a daily basis is all that bad of a record. Thing is, even when it was so worn that it needed a rebuild, and didn't have full power, it still would start right up and run if needed. That makes it reliable in my book.