Quote from Steve on September 19, 2026, 6:49 pm

Jamie has now received an email reply from Neil Williams, an Aden authority. He says

Hi Jamie

This question has been asked in The Dhow as well. These added letters occur when the Post Office has such a large load to process at the same time that the numbering on regular labels is not adequate to differentiate individual items -- in other words to avoid multiple items with the same registration numbers being in the tracking system at the same time. 

It is largely met with Aden on philatelic covers in 1937, notably Coronation FDCs. when the 'old style' rouletted sheet labels numbered 001-999 were in use, rather than the later perforated coiled type numbered 0001-9999. For Aden GPO I've recorded B, C, K, N, P & S all in manuscript and for Aden Camp PO K, T, JJ and KK hand-stamped and F & N in manuscript. I've seen many others in dealers' stocks. 

Registration labels are an oft-neglected niche area of philately!

regards

Neil

Thanks Neil for clearing things up. Your advice on my M Aden Camp Registration label is interesting and very helpful.