I wonder if the numbers he quotes are for a thin lens design. It seems the scope was sold in the past. There is mention of it in these forums.
The single lens corrector is interesting. There is a paper by Maksutov on a meniscus ahead of the focal plain as well as the normal form. No luck in obtaining it though. Only a part copy that doesn't cover that aspect. It can be bought of course.
Patents are curious things. I held a number via my job some in all major countries but I remember one that never made it into the USA as loads of completely unrelated patents were thrown against it. I suspect this can be a bit of a nationalistic thing or down to how the person who examines it feels on the day. In this case the patent may have got through because of the mention of a positive power corrector.
If he had said focal reducer he might not have got away with it.