Quote from pthy@ucdavis.edu on June 1, 2023, 12:02 am

Wiggins Teape supplied paper for aerogrammes for many countries, but perhaps not South Africa. Bechuanaland QEII aerogrammes printed by Bradbury Wilkinson used Wiggins Teape paper with the Gateway watermark with K, L, and possible I year letter codes. 

Does anybody have information on the meaning of the letter codes. I recall having see a list from Wiggins Teape, but can't recall where. 

Attached is an illustration of the Gateway watermark with the L code and also an example of the Bechuanaland aerogrammes.

Any help will be appreciated 

Peter