Trying do date metronome

I have this Wittner metronome and have been trying to work out how old it is. I’m wondering if anyone in your community can help, or point me in the right direction? Unfortunately the company says they lost many of their records during the war and when they moved, so they have been unable to help.
It is made of wood, I think pine or some other soft wood that was stained to look like mahogany. It does not have a bell. “1939” is written in several places inside, in pencil, in a European hand. However, according to Wittner there should also have been the initials of the workman and a 6 digit production number and it doesn’t have either of those. If 1939 is the correct date, it must have been made early in the year as they were not allowed to make metronomes later.
On the outside of the base, though barely visible, it says “£2 11/6” so it was obviously sold, maybe not for the first time, before decimalisation in the UK.
I think the badge on the front may be some help. From what I can tell online, the early badges were brass, and the more recent ones have the logo but no inscription. The badge on mine (which I think is tin) have the logo and “Metronom Maelzel—Made in Germany” written around the edge of the diamond shape.

I’d really appreciate any help you can give me in establishing the age of this piece.

Many thanks