Hi Rik, no sign of any C/S Mark by any of the War Office KB's. What would that indicate?
From the dates of despatch to the War Office it looks like the man from the ministry came knocking on BSA's door during the annual shut-down as a small number of bikes went from 26/8/39.
Then when the workforce returned they got to grips with the job and most requisitioned machines went on or around 4/9. A few still remained, being despatched up to 4/10/39.

My assumption based on the 1939 specs is that "C/S" indicates "Chrome / Silver" so standard civvy spec.

Purchases in August suggest that they were planned. Germany didn't march into Poland until 1st September.

Hi Rik, sorry, my mistake, "CS" is specified for all the KB bikes sent to the war office, the style of handwriting makes it look more like CP, which I was taking to indicate Chrome Plate.
just as an aside, around 80 KB machines were sent to Warsaw earlier in 1939, no doubt the Germans found them quite useful.