That's an issue with many of the blaberus genus. Discoids are almost always not actually discoids, but a hybrid mix of blaberus. I have a colony of pure discoids and the common stock(similar to how common hissers are hybrids usually) and they do have differences. The pure discoids seem to breed faster and are slightly smaller.
Deaths heads have a few different strains out there. Like Orin's, UCR, etc(tbh they all confuse me even haha). They have their differences, some are faster breeders, but not as pretty, some are larger, etc.
Blaberus fusca(dusky cave) might be one of the most underrated/unknown feeders there are. They are prolific and very similar to discoid. Main difference is the older nymphs and adults get larger, like between giant caves and deaths heads in size. So they are perfect for people with larger reptiles, but work just as well for smaller reptiles since the nymphs start off small.
Sorry I'm all caffeinated and on a roach rant!