There is another strange thing which I missed when I wrote the title post.
Book number 4 features another exlibris, which is crossed out. It is dated. The date is not crossed out, but, as suggested by color adjustment (shown in the Rene's page cited above) it belongs to this other exlibris (and not to that of Hořčický).
Since this other exlibris is crossed out, that suggests that it was put down earlier than the Hořčický's one. Its date is 1604. In other words, Hořčický could not put down his own exlibris for number 4 earlier than 1604. But this is two years later than 1602 for books number 7 and 18!
Possible explanation of all this: the number for # 4 was somehow "reserved", but not put down until after number 18. Perhaps the number was placed elsewhere in the book, but that piece of book got lost, so the possessor had to duplicate the exlibris later (and did it already as "z Tepenecz", not as "Sinapius"). The correct number could have been restored against a separate list of books which he possibly maintained.
Book number 4 features another exlibris, which is crossed out. It is dated. The date is not crossed out, but, as suggested by color adjustment (shown in the Rene's page cited above) it belongs to this other exlibris (and not to that of Hořčický).
Since this other exlibris is crossed out, that suggests that it was put down earlier than the Hořčický's one. Its date is 1604. In other words, Hořčický could not put down his own exlibris for number 4 earlier than 1604. But this is two years later than 1602 for books number 7 and 18!
Possible explanation of all this: the number for # 4 was somehow "reserved", but not put down until after number 18. Perhaps the number was placed elsewhere in the book, but that piece of book got lost, so the possessor had to duplicate the exlibris later (and did it already as "z Tepenecz", not as "Sinapius"). The correct number could have been restored against a separate list of books which he possibly maintained.