Ever since I bought my 69 SS I looked at the blocked smog tube holes on the exhaust manifolds and wondered same thing. Last year I researched it and found that the emissions requirements started in CA in 1966 and were in full swing for the 68 model year and beyond. Speaking for the 69 model year, if you car was a stick shift(any state), it had a smog system. This applied to BB's and SB's alike.
As far as the automatic cars were concerned, the cars could be equipped with smog systems and I don't know if that was mandated by the state the car was sold in or if that was optioned by the buyer. Seeing that most of those systems were removed promptly, I would think that cars with automatics were required by individual state laws to be so equipped.
I hope this helps. There isn't much printed information on this subject.