I saw him at the Share sometime around 73 or 74 when his band was the Caledonia Soul Express. No exaggerating, there were only about 20 people there and my singular memory of the evening was that a fight broke out among two of those ten people!
Never saw Janis there but saw just about every other Marin band/musician: Garcia, Van Morrison, Jesse Colin Young, Huey Lewis and John McFee when they were with Clover; Sons of Champlin, Commander Cody. I was there the night it closed down for good; all night party/jam.
as for the Lion's Share building I read somewhere it houses a company that makes medical or optical instruments....of course in the late seventies it was the location of Campolindo health foods.
Not sure about a Janis Joplin recording at Lion's share, but Van Morrison played there in 1973. At that time he could sell out basketball arenas, but a sudden onslaught of stage fright almost ruined his confidence in performing live. It was a double-bill performance at the Lion's Share that helped his career.
His 1973 Lion's Share show was broadcast on radio and is available for download here:
It's too bad more pictures and recordings don't exist considering the legendary artists and bands that performed there. Today, thousands of cars pass that location on Miracle Mile, not knowing the history of it. Is there anything in that building today?