Quote from pthy@ucdavis.edu on July 30, 2020, 10:10 pm

I came across a problem with WW2 airgraphs. I have been looking at Southern Rhodesian airgraphs and discover that the forms were only available at the post offices by paying the mailing charges (3d or 8d). The same is the case for the Christmas Greetings form. The rationale is paper shortage. 

Does anybody know how this was handled in South Africa?

In the GB, the forms appear to have been available for free, at least in the beginning. When the 1943 Christmas airgraph was introduced it was required that the postages was pair when asking for a form at the post office. Could it be that the forms after late 1943 required the purchase of a stamp with it?