Pete,
Congratulations, a lovely gun with a nice story to add! Just like JohnF, my M11 (1928 barrel, 11910) has a D mark on the front sight.
My frame is also 'in the white' but it has been reblued at some time! In the late 1930s the unit markings on the back of the frames were removed and replaced (in most cases) by the brass plates on the side
.
Reblueing was done over the filing marks.
Officer's guns usually didn't get the brass plates.
The grips seem to be GS replacements, produced at the 'geweermakersschool' in Java. Do they contain serial numbers or the GS mark?
I would expect that this gun was delivered with a later style magazine as the one shown. The Dutch found out that the spring catch was a bad idea in practice and retrofitted most with an extra locking pin (around 1927). After that they ordered regular style magazines with a locking pin.
Welcome to the 'dutch club'
Gerben