Steve, I'm with you on your explanation and here's a few more somatic mutations I know of other than the Casino (large fruited red ) to Casino Chips, one branch had cherry tomatoes. Perfectly stable as those here who have grown it already know,including me.
Yellow Riesentraube;ONE yellow fruit on a plant with all normal red fruits and the yellow is perfectly stable/
And two I saw early in my so called tomato career but didn't save seeds.
Green Gage, a pre-1800 variety that has yellow fruits, one branch had all red fruits.And in doing some Googling I found that way back there were both red fruited and yellow fruited Green Gage versions.
Dix Doight de Naples ( 10 fingers of Naples), fruits are red and kind of short stubby finger looking, if you will,and one branch had red fruits, but of an entirely diffent shape.
Maybe I can think of other examples, maybe not.
Carolyn