If you are referring to the dash numbers, model 10-3, 10-4 for example, they weren't always a frame variation. They are engineering changes to the model. One of the changes S&W revolvers went through was reversing the direction of the threads on the ejector rod. Another change was moving the gas ring from the yoke to the cylinder. Those changes would not have involved the frame.
There is no firm number of changes as it varies from model to model. The oldest models will generally have more changes. Many stainless steel models like the 64,65,66,67 weren't introduced until around 1970. Since these are just stainless versions of models introduced in the 50s, they were first produced with many of those changes implemented from the start. The current model 10 is a 10-14 I believe but the model 64 which is the same gun except in stainless steel is a 64-8 because it was introduced after many of the changes had already been made.
The main frame changes would probably have been going from a 5 screw system, to 4 screws then eventually 3 screws, and then there was a major change in the shape of the frame when they went to the transfer bar firing system and implemented the in frame lock.
The model 28 only went through 4 changes between introduction in 1955 and being discontinued in 1986. One change was reversing thread direction on the ejector which had no effect to the frame.
You folks are all talking variations on an assembled gun, but the article that I was reading indicated that there was a slight difference between the actual raw frame on K frames of the same era with the slight difference being made to accommodate a heavy barrel. Same or similar verbiage got to Wikipedia, see screenshot above... (See reference above for 10-1) Then looking at the model 10 variations list it seemed to support this as changes were made in quick succession in pairs and referenced heavy barrel and standard barrel. That had me looking to see what exactly was different, and so far I have not found an answer. My presumption is that the article was wrong OR that if there is indeed a difference then it is in the contouring so that a heavy barrel frame contours well to the thicker barrel profile.
