First question, why is there 4 sizes of piston

epc only lists 2 sets of rings, ones that fit the above 4 pistons, and a .5 oversize set.

Second question, when people get a .25 rebore, .25 of what ? .25 more than whats there, .25 more than what it should be, if so then which of the 4 above is it .25 more than ?

If theres only minimal bore wear, whats to stop having the minimum rebore possible and fitting a new ste of standard rings (aslong as its less than the reach of the rings 86.025)