Many thanks, Jon.
You're a goldmine of information. Were thespians pilloried in such a way prior to the 1930s? A good pointer might be to find the earliest version and look at the content. Later additions are often easily dated by contemporary references. The earliest versions I have access to are presented as from WWII.

If the song predates WWI there is a good chance we will never know its origins.

It certainly doesn't appear on broadsides or sheet music in any of the major collections.

Ploughing through contemporary WWI accounts might throw up some more detailed info but I don't know who has the access and time for this.