Hi Adrian!
Thank you very much for the quick reply! I thought it was a little earlier.
Which serial number is usually smaller? The case or the movement? The iwc database writes the date 1921 for the movement number 770 thousand.
If i write 770 thousand for case number, it gives two time intervals:
1919-1923 750,000-800,000 alte IWC Liste compatible with new case index of 2002
1920-1930 758,000-917,000 aktuelle IWC Liste compatible with old list from 2001
Yes, it's not an easy question. I assumed that it had to be adjustable from the crown. And i search wich calibers were in use, which were already adjustable from the crown.
The 52T has been in production since 1924, the 57T since 1926, and 65T since 1927.
73 and 77 could also be considered.