That's what I thought, but I've NEVER seen releases of the Dic dub in only two cases before. Ever. I wish there was a way to know...
Well considering those DVDs are for the Death Busters arc which was dubbed by Cloverway instead and released by Pioneer, and DiC stopped dubbing SM after R, the releases are bound to be different, different video publishing companies tend to release their products differently. So it's possible Pioneer released their DVDs in only 2 volumes. And if you look closely, on the top left corner on the front graphics there's a word printed on it, the letters are too small for me to make out definitively, but it seems to me like the word is "Pioneer". So that's another reason why I think those DVDs are probably legit. However I'm still not 100% sure though.
Why not just ask the seller if these DVDs are legit? Have you contacted the seller yet?
Btw the first 2 seasons of the 90s anime were released by ADV, in case you didn't know.