Do all koi have the potential to grow to 3 feet long?

I have never seen Koi advertised as any large type, although there are likely some genetic differences. In 25 years I have bought several Koi and raised a couple spawns. The adults have been 24 to about 32 " long in the same pond . My pond is only about 5 ft. X 10 ft. I have seen many home ponds , occasionally fish up tp 3 ft , they have always been in very large ponds. Also ,no pond owner has ever said they purchased large strains of fish. Also talked with a professional breeder ( he went to Japan to select breeding stock) and he never mentioned larger types. So , many Koi , but not all , will get to 3 ft , in a very large pond.