Have only just seen your message.
If you contact me at <peter@triumph.gen.nz> and let me know the engine number and following three letters on the crankcase, plus frame and gearbox if possible, I'll be able to say when it was assembled.
I'll also send a list of the booklets I've written covering various Triumph models, as one covers the Models CO and CTT. (I've almost finished restoration of my own 1929 Model CO.)
Peter C.
(Triumph specialist for the VMCC of Britain, but now resident in New Zealand.)