1951 NECO 20x110mm Navy Mk5 dummy

How early in the development is 1951?

The earliest one I have is from 1950. The headstamp is F A 50 and the only other markings are engraved on the driving band: LOT-FA-E-608-1951-20MM-T114

Edited once to include the following:

If you were interested specifically in the MK 5 MOD 0 headstamp, the earliest I have is 1952 (also from NECO).