So I'm wondering about fruit flavorings like commercially produced extracts and syrups?
My interpretation of the interpretation of the rules is that you can add anything you like, in any quantity and from any source, so long as any beer/mead/cider added was made by you (or perhaps by others in a non-commercial setting).
So commercially produced cherry extract, cherry syrup, cherry wine, cherry brandy, cherry concentrate are okay.
Commercially produced cherry beer, cherry cider, cherry mead are not okay.