First, I think we are learning that they'd fly for a gig, so I am not 100% sure this is a safe assumption that they would not have played NYC on 12/24 having played SF on 12/23 - especially for a special occasion.
Second, I just came across a piece from Hit Parader, attributed to June 1971, which includes the following: The Dead are anti "new politics", but "do help when they find an individual whose ideas impress them. For instance, on a recent plane trip across the country, the band met Huey Newton, leader of the Black Panthers. He told them his philosophy. They were impressed by what he said, as well as his personality. As a result, they agreed to do a benefit for the Panthers that was held in New York on Christmas Eve".[i]
Hmmm, she uses the past tense. Now, normally I'd poo-poo Hit Parader, but these things can surprise us. Any thoughts as to whether the GD actually played a Panthers benefit in NYC on Christmas Eve. 1970?
! ref: Ross, Penelope. 1971. Grateful Dead. Hit Parader, June: 10-12, 59, 64.
p.s. "Where Were the Grateful Dead" does better than "Where Was The Grateful Dead", grammar be damned.