I'm not an expert on saddlebacks at all, but I believe they are in the Clarkii family, and the clarkii family has a distinct body shape. They will be "rounder" and not as elongated as a B&W ocellaris. Also, the saddleback has a "saddle" where the middle bar extends along the dorsal fin. The B&W ocellaris won't have that.
Also, there is so much confusion in the hobby with naming. A "false percula" is a poor name for an ocellaris. It's a bad term that IMO should never have been, or should be used. It's like calling a "lab" a "false pit bull". Percula and Ocellaris are different species that appear very similar - hence the confusion to many. A black and white ocellaris is a color variant of the ocellaris species that is all black and white (although from talks with a breeder I know he has seen many behavioral and developmental differences that lead him to think they are actually a different species)