I just bought an old album page of Austria. On it were some newspaper stamps including this one from 1920:

Unlike all the others in this set, and all the others in my own collection, this is perforated. My Gibbons catalogue doesn't list perforated issues at all, and whoever owned the stamp previously had jotted on the album page, "perforated to order" - so I'm wondering what that means, and how come this stamp has perfs.
Examining the teeth, it's definitely been torn from the neighbouring stamps, so the sheet was all perforated at some stage, presumably not by the issuing post offices. I wonder how and why?