Wouldn't be surprised if a lot were multi-generational.
Mine is supposed to be a clone imported direct from Floricultura, though, so it'd only be multi-generational if they had cloned a clone. Can't speak to their practices.
This is what 'Sonia' looks like here (it is just opening).
I've just checked all the links in Floraculture with Summer in the name and none seem to line up to my plant visually.
Shirley..... on the Floraculture site doesn't seem to have spotting and the lip is different.
Sonia....the deeper coloured lines look the same but has no spots and as said the lip colour has solid colour area.
Selma.... Too white, no spotting and again the lip has solid coloured areas.
Suzy and Senne......not pinks
I think the comments about clones will be right. If its been out for 40 years who knows what has been done. So I'll use Summer Pearl on the label and just enjoy it for whatever it is.