Help with stock class names

[Rat Patrol]

I started a project a while back creating a list of the NHRA eliminations and winners from 61-69....which aint easy from a country where this info doesnt exist. !

Ive used a few reference sources, but I'm struggling trying to get an understanding of the class names.

I understand the weight break idea...but here's my question..

Larry Davis book talks about A/S , S/S and OS/S

Question 1 -

What I cant figure is where AA/S fits in the scheme of things?

Davis book lists winners in A/S and SS for the years 61,62,63. - but no AA/S

So when did AA/S come in...and why was it phased out in 67?

Question 2 -

Davis book lists no SS/A winners from 1968 onwards...the highest class seems to SS/B - Can anyone clue me in on what happened in 68?

Any help greatly appreciated.