If the date of distribution, etc., is unknown, a copyright date or a production date can be used as a release date.  If both the copyright and production dates are available, use the copyright date instead of the production date.  Precede a copyright date with the letter "c."  If a production date is used, make a note that the date is a production date.

245 00 $a New York City in a blizzard / $c Thomas A. Edison, Inc.

257 ## $a United States.

260 ## $a United States : $b Thomas A. Edison, Inc., $c c1902.

245 00 $a Smoldering sin / $c Roulette.

257 ## $a United States.

260 ## $a United States : $b [s.n.], $c 1925.

500 ## $a Date is production date; unable to verify if work was ever released.

If a copyright date or a production date is not used as a release date, it may be given in a note.  See 7B11.

See also:

4E.  Dates of distribution, release, broadcast

4.  Distribution, Release, Broadcast Area