What you have is a Field Post Office datestamp which would be issued for operational or other reasons to military personnel "out in the field". BFPO 1 was located in Hong Kong until 1997 and the FPO940 would be a CDS issued for use "in the field" or some location within the BFPO 1 area. The number value of the FPO would change but the BFPO number was fixed.
The image below is of a FPO cancel issued to the Royal Engineers during a display in Huddersfield, England and, in this case, the FPO was given the number 1015. Unfortunately the UK postal service thought fit to cancel it a second time


This FPO was given the number 991 which could be random or just next on the list but with other information can be associated with BFPO 22 in Germany...
