As a couple of owner/operators of the Goodberrys/Jigsaw group have been good enough to comment and clarify on the issue of their name change (and related product issues) I thought it worthwhile drawing further attention to their comments.
Particularly those of Cameron Walker here and here, and also Banvie here.
For what it’s worth I have done some research (*GASP* shurely not at RA???) and the addition of eggs would appear to be the salient difference between ice cream and frozen custard by any reasonable standard. Having done quite a few food science courses, the comments about the reduced air % allowing warmer temperatures (less headaches) sounds more than plausible.