As far as I know, no one in the Kaufman or Hart clan was the basis for anyone in the play. I think we all wish we had a Grandpa, Penny, and Mr. De Pinna in our families.
Certain unique books seem to be without forerunners or successors as far as their authors are concerned. Even though they may profoundly influence the work of other writers, for their creator they're complete, not leading anywhere.