Why was Secretariat always an "A" entry?

Just curious, why Secretariat was always post position 1A, 2A, etc. I thought that denoted a double entry by the same trainer, but am thinking that is not the case.

He would of been coupled with another horse. Riva Ridge maybe? Both horses would have the same owner. I don’t think many tracks couple entries any more.

He was coupled with Angle Light in the Wood and the Derby. Coupled with Riva Ridge in the Marlboro Cup. As for why he was listed as the second part of each entry, do they do an entry alphabetically? S is pretty far down the alphabet.

Some tracks had a policy of coupling horses with the same owner, and some with the same trainer (thus why D. Wayne Lukas had some craaazy entries in the Breeder’s Cup back in the 80s–I know they went to something like 1F at least one year). I thiiiink nowadays it’s only done if it’s the same owner.

Nowadays, most jurisdictions don’t couple owner entries in races over a certain value, it varies from state to state, some are as low as $50k, in NY the purse has to be over $1m.
Generally multiple trainer entries aren’t coupled anymore unless the trainer has an owning in interest in one of the horses.

Same trainer. For betting purposes mostly.
So in the 1973 Derby, you placed a bet on Secretariat that carries over to Angle Light.