I just received a note from someone on Facebook (Hi Synde!):

We’re playing Die Fledermaus at the conservatory this week and our parts have the San Jose Opera stamp on them. Am I playing on a part you marked up??

Ah-hah! I’ve wondered about this. Sometimes I find marks in my Opera San José book that are clearly not mine.

Update
… but maybe not! They are using only one oboe, so they might be using the combo part we used to use. Now that we have a second oboe I don’t use that book. Hmmm. I wonder!