In one of his articles, Sheldon mentions dishonestly in tire sizing. Tire manufacturers would make tires narrower than they were labeled to save weight on the spec sheet and sell more tires.

I acquired a pair of old looking Specialized Turbo LS tires. On the label they clearly say 700x25. On another part of the tire in tiny font the I.S.O. size of 20-622 is printed. The tires measure 21mm wide when mounted on my rims.

Any insight on this? It's not critical to anything, I'm just curious.