A *lot* of 70s Pyramid episodes fall under this category. I think Pyramid holds the record for most off-air constestant recordings etc. prior to when the holdings begin (June 12-16, 1978)
March 28, 1973 (June Lockhart-Rob Reiner) (First four minutes)
March 30, 1973 (June Lockhart-Rob Reiner) (Second win in history of show)
June 13, 1973 (Kaye Ballard-Richard Deacon) (Preston has said he was the one who recorded it)
March 1, 1976 (Anne Meara-Nipsey Russell) (Sue Dolleris recording)
April 20, 1976 (Marion Ross-Larry Linville) (4 minute clip of Winners Circle)
November 2, 1976 (Phyllis George-David Groh)
November 3, 1976 (Phyllis George-David Groh)
February 9, 1977 (Adrienne Barbeau-Jack Carter)
March 31, 1977 (Carole Ita White-Ron Glass)
September 12-16, 1977 (William Shatner-Leonard Nimoy) (Full week)
October 28, 1977 (Rita Moreno-Tony Randall) (Winner's Circle Only)
February 24, 1978 (Anne Meara-Nipsey Russell) (Marc Archembault recording)
February 27, 1978 (Joyce Bulifant-Ron Glass) (Marc Archembault recording)
April 28, 1978 (Adrienne Barbeau-Soupy Sales)
The two 1976 shows that have been in the hobby (Loretta Swit-Clifton Davis; Jo Anne Worley-Tony Randall) I believe were "rescued" archival master tapes.