When the country of production is unknown, use the abbreviation "S.l." (sine loco, without place) enclosed in brackets and, if necessary, give further explanation in a note.  See 7B12.

245 00 $a [Brook Collection. $n No. 15, $p Bullfight-- unidentified works] / $c [production company unknown].

257 ## $a [S.l.].

See also:

3C.  Country of production

3.  Country of Production Area