Hi Anneka,
I am not an expert, so I won't asses on that piano. However, thanks for digging out this old conversation, which is quite interesting.
Let me try summarizing what the discussion was about.
Contribution #1 presented a photography of a Zimmermann grand with serial #200733 and asked if this is really a Zimmerman because it looked so much like a Steinway M-170 and serial number suggests that it had been built in the 1960ies, although it was apparently from the 1920ies. Contribution #5 shows more photos of that instrument.
The following discussion was mainly speculations, such as that this instrument could be an original Steinway M-170 which was modified in the GDR to hide that jewel from the officials, or that Zimmerman had assembled that instrument from a spare Steinway frame, and so on.
Later on, user agraffentoni came up with information of two very similar Zimmerman grands with serial #200951 and #201182, which are clearly dated 1928 and 1929 (by pincil inscriptions on the c5 key).
So it seems the conclusion was (although not explicitly stated in the conversation), that Zimmerman has built a Steinway M-170 clone in the late twenties of the last century and surprisingly introduced a separate set of serial numbers for it.
Since your instrument seems to look very similar to the others introduced in the conversation, yours may well be one more of that series. The inscriptions on the frame as well as the serial number, which is rather close the the three others mentione above, support that assumption. Is yours 170 cm long?
About prices ... dunno what it'll be worth. That's up to you
Cheers
- Karsten