Well I have found 3 BBFUN with mentions of a 20th gig.
1 August issue. Mike mentions a show being planned. No venue at time but all ex band members to be invited plus the Captain and Tennille plus Sonny and Cher.
2 November issue. Al and Brian confirm gig New Years eve at Inglewood. (Not Long Beach as I had thought.) Two stage sets planned. One a beach scene and the other a giant turntable. Both to be used on tour in 81 but one at a time.
3 February issue. Short mention of Star on Hollywood Blvd December 30 plus gig the next evening. Mention of 3 songs seldom performed live at the time. '409', 'Surfin Safari' and 'I Can Hear Music'. Jan and Dean plus American Spring joined in at the end of the show. A few photos of the gig are of poor quality and 'reprinted by permission of Brother Records'. The usual concert shots but one of Al wearing a early BBs striped shirt of interest. One long distance shot of private party held at the Berwin Entertainment Center, (now The Hollywood Athletic Club I believe) in a giant pool. No individual members or associates in view, except Ed Roach naked in a palm tree! (ok...I made that last part up
)
No mention anywhere of gig or party being filmed.
I also recall reading something about why the gig was happening in New Year 1980 and I think Mike mentions the band may have broken up by New Year 1981. I guess with Carl planning his album doubts must have been raised about The Beach Boys future.
As an aside. One old issue mentions Dennis hurting his hand playing drums during a concert in Detroit during 1980. Any more details Ed.