Would I be correct in understanding you are referring to the serial number on the butt of my 1905R rather than the number on the bbl?
Yes, I was referring to the butt number 422X, but they encompass both.
Closest below is 337X. Closest above is 502X.
I also have 1905-E # 428X, (different animal but marked in the same manner) which is very close to yours.