Variable fruit shape

[duajones]

From what I have seen in my garden and reading through many posts, it appears that variable shape in a variety is pretty common. The one that has been the most variable for me is Cherokee Purple. The first two years growing it were in containers and even though production was very low, almost all of the fruit was beefsteak shaped. Last year, first time in the ground with the variety and almost all of the fruit were standard shaped and maybe even smallish for the variety. This year, 2 different plants and 1 is predominantly beefsteak shape and the other standard.
I havent had any yet this season but taste has been pretty consistent in all of my previous grow outs. Is the variable caused by the parent plants? Just Curious