I think the other is referred to as Black Twig - Paragon. I love this apple and grafted the Mammoth version a few years ago and hope to get an apple to try next season. It is a hard, heavy, crunchy tart apple. What's not to love!

Your question reminds me of the King of the Pippins vs. Reine des Reinettes discussion.

Thanks q! Using your info & googling "black twig paragon" I was able to find some info. I gather the debate whether they're the same or not has been going on since the 19'th century. Seems they're slightly different, at least the size is, maybe more.