With that in mind, I did want to put down this little tidbit I found in the Grateful Dead Archive at UCSC concerning the December 4-7, 1969 Dead shows at Fillmore West (1). I can't remember if there are additional pages of this in the folder, but there's a handwritten page which looks basically to be a handwritten (not sure by whom - Lenny? Rock?) contract addendum, probably drafted early December sometime.
Condition. In the event of a free concert, it is agreed that the members of the Grateful Dead and the members of Fillmore West families will participate in said concert and hereby forego the Saturday evening [12/6] performance at the Fillmore West. The Grateful Dead will forego $2,000 - and no comps for Saturday nite.
Condition. Because of the extraordinary circumstances surrounding this coming weekend and the presence of the Rolling Stones, Terry Reid parties -- also the homecoming of the Jeff Plane -- it is hereby requested that the promoter provide the Grateful Dead 75 more comps.
Request. That in the event of a free concert, the Grateful Dead and the Rolling Stones hereby request permission to use the premises of Fillmore West Saturday nite for a private, by invite only party -- the most memorable evening in San Francisco ballroom history!!
Ahhhh, what might have been!
(1) Grateful Dead Archive, Special Collections, UC Santa Cruz, ms 332 Series 2: Business, Box 2, Folder "Contracts - Fillmore West, December 4-7, 1969 - Production".