needs further investigation I think
I am not so sure the OP has a 4th change. From the OP's pictures the barrel caliber stamping is on the LEFT side of the bbl (I can just make out the "G" from CTG and the ding bat). Also from the one pic it appears the OP's gun has the "divot" in top strap (could be photo reflection, but looks like maybe the divot)
My 5", 5 screw 4th change (s/n 105093) shipped October 1921 per Roy Jinks and has dingbat "32 W.C.F. CTG" dingbat on RIGHT side of bbl, and NO divot. Mine has NO "made in USA" anywhere, and small S&W logo on left side of frame. No medallion, checkered, diamond grips appear correct on OP's gun as well as mine, but even with strong light I can't find any remnants of a penciled number.
I found some posts about the "divot" but can't seem to bring them up now. Is the OP's maybe a 3rd change?? Do we know for sure when the changeover was made and if there were some "transitional"?
All in all.....a nice pickup for $400, hopefully you can find some cowboy action loads and have fun shooting....they are a hoot.