In the 1980's (?) I believe Schweizer came out with an "update" to all their flight manuals stating "Aerobatics are not approved", mostly to cover themselves "in case someone pulled the wings off, etc.".
Having an old manual does NOT mean you can "do what you want" since the FAA would look at the current MFR manual.
;-)

Aerobatics not authorized per a SB in 1987, covering most (if not all) of their sailplanes.