Can you expand on the dividing by 2 ?

I had a 4 row 7000 that was a 1976 model I'm pretty sure it had long link chains and large tooth sprockets. So the charts in the original book would be direct setting and populations correct ? I remember some of those corn pop settings as shown in these charts and never divided by 2 ? I'm pretty sure friends planter is still original with long link chain and large tooth sprockets also which is why I was interested in seeing an original chart. 

I thought there was discussion on here of later manuals having different settings and different number of tooth sprockets. It was in those cases where regular roller chain and smaller tooth sprockets had replaced the originals that you needed to divide by 2 to get back to the original settings ?

Just want to make sure I have the correct information and reasoning on this to pass on.