The Book Switch Theory

[Jorge_Stolfi]

one could randomly select a few other historical figures (or at least one such figure) who also received the ennobling title “de Tepenecz” (or a similar honor) 

I seem to recall that "de Tepenecz" was a title that Rudolf created specifically for Sinapius, and Tepenecz (Tepenec) was a relatively small bit of land with only the ruins of a castle that had been destroyed around 1390.  Since Jacobus left all his property to the Jesuits, I suppose that he had no heirs.  So he must have been the first and last of the very illustrious line of Tepeneczes.

and who left behind some number of ex libris signatures. Samples of their signatures could then be compiled. The goal would be to show that other individuals likewise exhibited a range of variation in how they formed their signatures

I suppose that an ex-libris generally has the name of the owner, not his signature, and may be written by a spouse or employee.  Thus I expect that there will be examples with substantial variation of handwriting, language, and name.

But I think there will be very few examples where the person's ex-libris included a sequential number written at the same time as the name.   There must be many people who, having gathered or inherited a large library, decided to make a catalog for it, which implied numbering the books.  But then the numbers from 1  to several dozen would be written all at once, by whoever compiled the catalog.

And I expect that there will hardly be a case where ex-libris #4 and #19 have exactly the same form of the name, in exactly the same handwriting, while #7 and #18 are as different from those two as they could be...

All the best, --stolfi