What a great time I've had on a snowy day...
After some more reading about, it looks like this, and the other recordings from this show were made 12/15/1974 at the Record Plant in Sausalito. The band, at least this one with Bob Welch and Doug Graves was basically defunct as of 12/5. Mick was already looking at Lindsey Buckingham by this time, he and Stevie Nicks would join the band New Year's Eve two weeks later.
Reading on, it says Graves was actually offered a full-time job in the band, as backup for Christine, but it was decided later on not needed. Quoting-
In late 1974 Graves was preparing to become a permanent member of the band by the end of their US tour. He said:
I'm looking forward to adding something to this already great band. I helped engineer their album 'Heroes Are Hard to Find' and got to know each member well. It came to me as a shock when Mick asked me to join but I am enjoying playing live with the band, and hopefully will start a new studio album with the band soon.
However, Graves did not ultimately join full-time. In 1980, Christine McVie explained the decision:
He (Doug Graves) was there to back me up, but I think it was decided after the first two or three concerts that I was better off without him. The band wanted me to expand my role and have a little more freedom, so he played some organ behind me, but he didn't play the same way I did.Here is Sentimental Lady > Future Games from the same set.
*Alas, it said nothing of the BSB pickups in John's bass... were they the originals and the black ones replacements?