My guess has been that at least some, if not most, post-1930 .32-20 shipments may have been made up of parts in inventory remaining after component production ceased. e.g., if an order came in from a distributor or retailer for .32-20 M&Ps, and all parts were available, S&W could have simply assembled and shipped it/them until the inventory was exhausted. As previously said, there are a fair number of .32-20 M&Ps in the SN 14xxxx range known to have shipped in 1930-31, strongly indicating that new production ceased around that time, and even possibly a little earlier - note that SN 141399 shipped in 3/28. Unless there are factory records providing the date when .32-20 parts production ceased, all we have is conjecture. But assuming that the end of production was around 1929-30 is probably not far from the truth.
I believe that Colt may have continued .32-20 revolver production until somewhat later than S&W. I have a near-mint .32-20 OP which, according to its SN, shipped in 1936. I also have a pretty .32-20 Army Special with a 4" barrel, but it's from around 1911-12 as I remember. I haven't seen that one for a long time, it's just too nice to shoot. I probably should dig it up.
