Pkay,
You're losing me, here.
The Model 29 is still in production.
The Model 629 is still in production.
The difference is stainless steel and a full underlug on the 629.
The basic gun remains the same. The lockwork, frame shape, etc. is essentially the same as it was in 1950. There have been some minor manufacturing changes, and of course the "strengthening" that was done in 1988 for the .44 Mags., but essentially the same process has been going on with the Python.
Essentially cosmetic and minor engineering changes that don't affect the overall design of the gun. I can pull the trigger out of a 1960s Model 29 and drop it into a 1990s 629 and it will fit, and work (but as with any replacement critical part, may need a little fitting).
By the time the precursor of the Model 27 came about (the original .357 Magnum, as it was known, in 1935), the N-frame had been in production since at least 1908 in the following calibers:
.38 Special/.38-44 (.38/44 was the same as the .38 Spl., but loaded to much higher pressures. Essentially, the first .38 Spl. +P.)
.44 Special (the original chambering for the New Century Triple Lock)
.45 Smith & Wesson (pretty uncommon). I got to fire one of these a couple of years ago.
.45 Colt (fewer than 50 are known, very valuable)
.455 Webley for shipment to the British & Canadians during WW I.
.45 ACP, for use by the US military as the Model 1917.
Supposedly there were also some made in .22 Long Rifle, but I've never seen one. I suspect they would be quite valuable.
There may be other calibers that were also chambered in N-frames prior to 1935, but I don't have my books at the office.