The S was from
A 17: A mark of a man of letters? (6)
(S) _ G _ E _
Which I have as Signet
The A from
A 19: Theatrical poster revealing cost of dramatic production?(8)
P _ (A) _ B _ L _
Which I have as Playbill
The E is from
A 21: Extremes of grin by, and about, youth leader annually (4,2,4)
Y _ _ R _ O _ (E) _ R
Which I have as "Year to year"