Unfortunately there are no Masterpiece databases on the S&WCA website but I did find some ship dates on this forum.

S&W made frames in batches (back then) so what is 'normal' for a M19/66 is not for other target K frames.

Round butt M19-5/66-2 show up at 98K and 99K, square butt M66-2 at 100K and SB M19-5 at 120K.

I did find that 263K8xx is reported to be a 15-4 that shipped in 1984. If the -5 change on the M15 only eliminated the barrel pin, 263K is way into where I would expect to see the change and two years after too.

The lowest "-5" I found was an AUH that shipped in 1986, when the 6 and 8 3/8 barrel were introduced. Is this the same time frame as the switch to the wide rib HB?

Anyone out there have a M15 between 100K and AUG and then AUH ~ BBF (dash 6 for M19)? Is it stamped -4 or -5 and is it a narrow rib (tapered barrel, right?) or wide rib heavy barrel?