Thanks very much guys!
I think we're making great progress.
I had focused so much on the overprint that I hadn't realised some basic aspects of these stamps:
- There seem to be 30 different designs, split over two sheets.
- The stamps are split into 10 postage and 20 airmail.
Here's the same bottom left section of my only other sheet like this.
This has a few differences:
- Values are 16 to 30 bogdaches (rather than 1 to 15 bogdaches)
- These are all airmail (rather than the first ten postage and the rest airmail)
- No overprints on the stamps or in the margins
- CTO rather than mint
Both sheets are perforated.
I'd guess then based on your info that I may have two Michel blocks corresponding to:Mi 693A-707A CTO
(assuming A = perf, taking the next 15 numbers for the 16-30 bogdaches sheet from the English language catalogue and the image is from the later set as Rod has suggested)Mi 999A-1013A mint
(assuming that A = perf and the numbers from the German language catalogue)
Does this look reasonable?