Horčický's books

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IMHO they're all the same person. The letterforms change on a continuum rather than two (or more) distinct hands.
   

In the first two above the name is penned quite similarly save from the horizontal crossbar on the J, which is sometimes drawn in a single ascending clockwise loop, and other times with a stroke of its own. And this is not internally consistent: In his B&W signature the J crossbar is drawn in a single looping stroke, whereas the T has a distinctly horizontal stroke. In the last picture we see again the crossbar on the T, this time disjoint from the ascending stroke due to a lack of a pronounced connective loop.
In the VMS signature on the other hand, it's the J that's crossed with a horizontal stroke, and the T isn't. But the general slant and slope of the crossed T closely matches the VMS' J's body.

The p letterform also is drawn counterclockwise in a single loop, the fact that it comes out more angular or curved can depend on the circumstances (cramping of the hand, slant, angle of the paper, speed of writing). I highlight in turquoise on the right picture what I believe is an intermediate form between the angular p and the more curved p we see on the VMS and first two signatures, but the fact remains that all p's seem to be drawn starting at either the previous a's endpoint or at 11 o'clock, go down counterclockwise at 1 o'clock and then descend, with an optional final flourish that loops clockwise and ascends diagonally at about 2 o'clock angle, just like his S and J.

As for the rest of the letterforms, they seem roughly consistent except for maybe z which has two variants. The B&W letter b is drawn with a connective stroke from the previous u, but the rest of the letters are similar to the other examples; I don't think it'd make the case for a separate hand.

But we'd need a larger corpus before jumping to conclusions IMO