Essays exists suggesting an overprinted 1d lilac for use in the British post office in Crete following the international occupation, mounted as a single of each on a card (The Overprinter 1982/2 p.26, ex Robson Lowe auction; reauctioned 2008 by Collectio). These are presumably authentic, but were never issued.

(Image courtesy of Collectio auctions, Greece, sale June 2008)
The overprints read:

ΠΡΟΣ. ΤΑΧ 20 ΠΑΡΑΔΕΣ ΗΡΑΚΛEΙΟY | ΠΡΟΣ. ΤΑΧ 10 ΠΑΡΑΔΕΣ ΗΡΑΚΛEΙΟY |
(abbreviations for ΠPOΣΩPINON TAXYΔPOMEION ΗΡΑΚΛEΙΟY = “Provisional Postal Service of Herakleon”)
The card bears the intriguing message “Don’t press too hard”, which may have been an instruction not to press the handstamp too hard (it is rather blurred) rather than a request not to push for the issue if political niceties were sensitive. They were not discovered until 1977 inside an OHMS envelope.
These items are also covered in GBOS Levant Study Paper 1 (Appendix).
References specific to this and related chapters
GBOS GB Overprints Compendium edition 8, Dr John Gledhill (12/4/2020)
Particular thanks go to Stanley Gibbons Ltd, for permission to quote their catalogue numbers and numerous other contributors who are mentioned in the Appendix section.
All content is copyright, Dr John Gledhill and the GB Overprints Society, May 2025.