FYI I found a date being 1907 and asked around.

The fact that the term "levering" is used could mean that it's made in the Flemish speaking part,
being Belgium or the Netherlands.
But, the 2,5 denomination isn't used often in Belgium (none so far) nor in France (before the euro).

We have 3 languages in this set
the box: Dutch or Flemish
the mother of pearl: French
the metal token: German

We have 3 official languages in Belgium
Dutch/ French and German.

I think saying that it's from around Belgium is not so unlogic.

BUT, no proof and no idea what the O stands for.

Not done with the box but getting there. The outside turned out possible to save. Just some last details on the outside.
The inside I would like some "time period" correct upholstery to protect the mop.

Jo