Germany: Questions About "Hausauftragsnummer"

The pane pictured below was identified by the seller as Mi-HB32, but I have yet to verify it. I purchased the pane because 1) the price, and 2) the number on the left selvage known as a "hausauftragsnummer".

I originally thought these numbers were plate numbers, but I have also heard these called "order numbers" - which is what the aforementioned German word translates to.

What exactly are these numbers used for? Who ordered stamps in quantities large enough to justify a die change during printing?

I'd love to learn more!

Brian

Hi

In this case, H 7592 is the order number, the production order number of this particular printing work, and 20 is the year (1920)