ha! i love learning about these things! i will check my latch immediately for the undercut. i had about determined that the round sight was the last thing to go. i have an improved i-frame 32 with magnas (numbered to it) that has the later sculpted latch, so i am thinking the last sculpted latch was the "next to last" thing to go.
we pretty much know when the 4-line address starts to appear.
i figure the left-side-only barrel address was the very first thing to go. i have seen it on several 2-inch m&ps that lettered to 1946, and very, very seldom see it on small frame post-war snubbies.
i figure the fine checker/square-corner grips were the next thing to go away, and the early latch right about the same time.
i'd say that shortly after that the round corner grips were completely replaced by the small magnas. i don't think i have ever seen anything with service grips on an improved i-frame.
then, i think the latch was changed to the first iteration of the flat latch.
then, the round sight. i have definitely seen flat-latch/magna guns with the round sight.
with all that speculation (!), we KNOW when the chiefs appeared, and the very first ones had the round sight, later (3rd?) sculpted latch, and round-corner small service grips.
i honestly think that the very earliest production of the chiefs was literally using up the very last "early" stuff in the bins. very, very quickly the chiefs were in basically "modern" trim (magnas, flat-latch, and ramp sight).
i think the chiefs are so rare as to not be of much help, and about the same with the 32s. where we could really check on overlap and funky combinations is with the terriers. they were in full production well before the war, and, i suppose immediately after civilian production cranked back up. right through these interesting transitional years. them having their own serial sequence is helpful, too.
if they just weren't so stinkin' hard to find! i have carefully looked over two prewar (one-line) terriers, one from 38, and one from 39. both had the black hard-rubber grips, and both had been subject to very stinky refinishes!
anyway! those are my humble observations/speculations. as i said earlier, this is a very interesting area of s&w modernization/transition. i honestly THINK that they were thinking about snubs immediately after the war. i think they played with 32s very quickly, almost surely in 1948. maybe even bouncing around in heads as early as 47....or 46!???! then the chiefs appear, pretty much stretching the "little snubby" envelope to the max, with a brand new frame, and a full-power cartridge. the chiefs finished off the early features probably within a couple or three weeks, at most. maybe just days!
at any rate, a tremendous amount of change occurred at a pretty quick rate! finding new combinations is extremely exciting to me. i about hyperventilated when i ran across the early 32!
good grief! it doesn't take much to get me excited any more! i am getting old!!!
Now if I could just find a shooter grade example like your Terrier, I'd be a happy camper... until my next "gotta have one" discovery struck! 
It is well worn but not abused, the grips are of the original type, but I'm having hard time making out the number stamped inside. This example has the serrated ramp front sight and the second style flat latch and bears serial number 42XXX. It's still early enough to be a 5 screw. I know I would be happier with a true Post-War Terrier, but this little guy just jumped up at me and the owner cut me a deal appropriate to the finish. Anyway, it came home with me and is getting to know its older brother the .32 HE Snubbie that started this thread. So far it appears that they will play nicely together and be willing to share the same holsters and gun rugs. 
