Looks like the drive sprockets stayed the same but early models had aluminum road wheels and then they switched to steel wheels .
I guess Tamiya molded the road wheels and sprockets as sets , so there is a twin set of sprockets .
The other road wheels are different , yeah ?
Drawings at the bottom of the page showing the difference in appearance between the aluminum and steel road wheels :
https://tanks-encyclopedia.com/coldwar/us/m60_patton.php