Thanks for that Lance. We seem to have drawn broadly the same conclusions! And I am speaking from memory, which is often faulty - it could well have been an AV prefixed rifle that was dated 1944. Interesting that you have not come across any AY or AZ rifles either.....

The multiple production lines each with allocated batches of rifles for conversion to 4T would explain the blurring of the change overs.

Out of interest I have only seen one R prefix 1944 dated rifle, most being 1945's.