The football cut appears almost the same time as the introduction the Combat Magnum in late 1955 early 1956 (Coincidence?) Im assuming between the longer .357 cartridge and longer K magnum cylinder the idea was a football shaped relief cut in the stocks would allow extra room for case extraction but its only a theory, The football cut changed to the "speed loader" relief cut in the very late 70's to early 80's and allowed more room for use with speed loaders.

The feature that changed around 1963 was the shape of the checkering , older versions have a sharp transition from vertical to horizontal at the corner of the heel where the later versions have a rounded transition like yours.

As stated they are very nice stocks and its such a minor thing most would never notice , My S&W OCD meter is set a bit finer so these little things tend stand out.,,,Sorry to say it can be an illness