"I did not see any mention of a single NDCA manual"

Not a manual, but they do publish a syllabus list of steps in their rulebook, however in most cases I think they also allows the lists of the member organiations to be used as well.

Have judged many comps in the states , from Prof. Champ.to pro/am , in all genres.

We allowed the usage of all Br. variations in the Smooth div. ( W-FT --T )from any of the Indies and chains, were acceptable . Rhythm dances followed a similar path .
Silver "closed", had guide lines, tho a little more blurred than Br.

The 2 major implementations that came into play in the 70s--- spin turn was brought into the Amer Syl. in Waltz-- plus -- most everyone started to use the Intern. style link to create prom. in Amer style tango ( which I still disagree with )

The " council " compiled a manual at each level--- Br, Silv and Gold ,that was " recommended " for usage by all comp. dancers in open comps ( to the public at large )

Ricky Geiger,among others, collaborated on the tomes . This was done in the seventies .

NDCA-- I was an examiner in one of the National Soc.for many yrs . -- and yes -- there were manuals that were produced in collaboration . ( they didnt fare very well )