Hi nigelc
Quote:
However, I believe I've found the postmark: EREN-KEUY, Erenköy, a suburb of Constantinople / Istanbul on the Asian side.
The reference and picture are in the last addendum in Volume 4 (Turkey-in-Asia) of Coles & Walker so I'm glad I started looking in this volume.
This has the right format including the large figure 1.
Not sure if this is the same postmark as listed in Coles & Walker as I do not have a copy of this publication

The above is from PTT Muzesi Osmanli Posta Damgalari Katalogu – Dr Hidayet Yavuz Nuhoglu – Talip Mert printed in Istanbul 1990. The quality of the printing is poor as I believe all the postmarks in this catalogue was taken from post office record books
Andrew