Polo Popular, BUR? dating?

another dating ...

This lamp is designed by Christian Dell, model Polo Popular.
This version in the photos that goes back years? Doing a bit of research I found other slightly different versions:

- The base does not mention the brand (usually BUR)
- The joint between the base and the arm is different than other models (it is shortened)
- The ring that locks the arm to the base is made of bakelite (in other models is in chromed steel)

In the publication "Die Metall Werksatt... of the Bauhaus Archive is reproduced exactly like mine, describing her as being produced in 1931, but I'm not convinced!

everything looks fine for me.
the inside grey laquered shade seems to be right as well for 1930s production. i've owned a polo popular just marked BuR once ago. it seems to be that different iron foots existed and used at the same time....