In addition to the placement of the logo, I've always been curious about some other of the stamping, specifically the "Lazy Ampersand" that appears both on the barrel and in the stamping on the right side of the frame forward of the trigger guard. Some guns will have it both places, and some only on the barrel but not the other spot, and still others have a "standard" ampersand in both places. I felt is is the older guns with the lazy ampersand in both spots, and it changed at some point gradually, same as when P&R started disappearing.
Case in point is bill-in-texas's 1973 ship date M28-2, which was probably made in 1971 or 72, because it has a 5 digit N prefix; I can see it has the standard ampersand in both places, but my M28-2, made in 1973 (six digit "N" SN starting with '1') has the lazy ampersand on the barrel, but not the frame, and even though it came with magnas, the S&W logo is stamped higher on the side plate.
If there is/was a logical progression of these changes, I can understand it, but seems like it goes back and forth a bit