Creating flashcards with LaTeX

Question

As the current semester is almost over and my lecturenotes-typesetting project draws to a close, I start learning the definitions with flashcards. I've created the flashcards automatically with a Python script that extracts \begin{definition}..\end{definition} and puts them into a new TeX-document. In most cases, it works fine:

The TeX-file is in A7 so that every page contains exactly one definition. To make sure that this works, I surround the definitions like this:

\vspace*{\fill}
\begin{definition}..\end{definition}
\vspace*{\fill}
\clearpage

I've inserted the \vspace*{\fill} to center the definitions on the A7 page. So I can print 8 definitions on A4 pages and cut them (see image below).

This works fine for about 60 flashcards / definitions, but about 10 flashcards are either not vertically centered or have 2 definitions on one page.

Why are there pages with two definitions, when after every definition is a \clearpage? Is there a better way to vertically center definition environments than by surrounding them with \vspace*{\fill}?

(I don't think you need to look at the Python script or the TeX-template, but if you want to, you can.)