Unfortunately, it appears the shellac became standard for the 91/30's at some point prior to WWII. When exactly it began I have not been able to determine. Earlier models had an oil finish and those provided to other nations such as Spain had an oil finish.

So WWII correct 91/30 will have the shellac as best as I can determine.
Information
Warning: This is a relatively older thread
This discussion is older than 360 days. Some information contained in it may no longer be current.