If the distributor is unknown, give the abbreviation "s.n." (sine nomine, without name) enclosed in brackets and, if necessary, give further explanation in a note.  See 7B11.

245 00 $a [Slapstick comedy--unidentified works].

257 ## $a United States.

260 ## $a United States : $b [s.n., $c 191-?]

See also:

4D.  Name of distributor, releaser, broadcaster

4.  Distribution, Release, Broadcast Area