It wasn't until the middle part of the 20th Century that Vacheron
Constantin knew that its founding was in 1755. They had been going on
the knowledge that the firm was founded in 1785. Therefore, 1935 would
have been a the 150th anniversary of the firm, and may have been
honored with some watches commemorating that Jubile year for them.
However, marking the movement with "Jubile" seems like a too subtle way
of doing that.
That is just my best guess. I will forward your question to someone at VC to see if my guess is correct.
Bill