OK... Genome online DB (Radio Times listings) has 2 items for CFOF that include Sandy Denny:

Saturday 18 March 1967
17.31A CELLAR FULL OF FOLK
with THE IAN CAMPBELL FOLK GROUP
SANDY DENNY
CLIFF AUNGIER sings and introduces on record Tom PAXTON
Produced by Ian Grant

Saturday 22 April 1967
17.31A CELLAR FULL OF FOLK
with SAM'S FRIENDS
SANDY DENNY
Bill Clifton sings and introduces on record THE BROTHERS FOUR
Produced by Ian Grant

(full list abtainable via https://genome.ch.bbc.co.uk/search/0/20?adv=0&q=cellar+full+of+folk&media=all&yf=1923&yt=2009&mf=1&mt=12&tf=00%3A00&tt=00%3A00#search)

It seems these are not LFSC despite earlier reports to the contrary in some sources...