Wow, somebody is old enough to remember Washington Square and the Sunday sessions. Roger Sprung (and his brother, George) were there but I think that Lionel Kilberg got the permit. It all started back in the mid 50's. Lionel lived in a crowded loft on Ave.B. Other regulars included Jerry Silverman (who wrote the Folksinger's Guitar Guide), Eric Weisberg, Steve Mandel (They played the banjo and guitar parts for the movie, DELIVERENCE), Mike Cohen (Guitarist for the Shanty Boys) and his brother John (The New Lost City Ramblers), Tom Paley, Roy Berkeley and, if memory serves, Cynthia Gooding, Dave VanRonk, Mark Silver, Artie Rose, Harry and Jeanie West, 4 String Arnie Feldman and a host of others who made my teenage a joy.
Later on, in the 60's, Tom Paxton, Marc Spolstra, Phil Ochs, Bobby Dylan and Buffy St. Marie immigrated and politicised the sessions, which was appropriate to their talents and the tenor of the times.