Rotor thickness minimum 4-piston KH?

If you have to buy new rotors, get ones where the 'hat' that goes over the hub has been machined. Every time I've checked the castings all seem to be the same - which means the as-cast hat will kiss the pistons boots every rotation. :(
if you find really old stock, that's different. I first noticed this in the early to mid 90s so I mean really old stock.