I have read here that there where two actor that played George's dad. I think people are confused with Jerry's dad who was played by two actors. We will see when the DVD's come out, and if I am wrong I will admit it.

There were two actors who played George's dad Kramer. The first was the original actor, John Randolph. He played George's dad in episode 62 - The Handicapped Spot (where his car gets destroyed when George parks it in a handicapped spot). He was then replaced with the Frank we all know and love and his scenes were deleted and re-shot with Jerry Stiller. See below site for description.

I have never seen the show with the original Frank since he is not in the re-runs, maybe that is why you concluded there was only one Frank. As for "Other-Morty", he is still in the re-runs for some reason. (Just to torment our friend Maestro, I think).

http://www.tvtome.com/tvtome/servlet/GuidePageServlet/showid-112/epid-2302

The original Frank

It looks like there is an over abundence of evidence on there being a second Frank. I will go ahead and do like I said I would, and plead 'no contest'. I was wrong.

You can learn alot by sticking around here. ;)