BigBoku, does yours have the white outline rear also?
They certainly didn't seem to be too common but I have seen more than a few. 6K612xx has the RR/WO.
By the early '60s at least, most likely earlier, they showed up in the catalog as an option.
When they started using the six digit product codes in 1984, there was one for a 2.5" 19 w/ RR/WO; 100703 (blue) and 100715 (nickel).
It's 1972 (3K101xx) but I have a Model 19 with a red insert and white outline rear sight blade.
Catalog excerpt