This is from an old site that was up before the 94 ban ended, only thing I ever saw on benelli preban serial numbers.
Benelli (imported by H&K)
I called H&K and they couldn't/wouldn't specify the "cutoff" serial number for pre/post ban Benelli's. Given this, the best we can do is post assorted serial numbers and import dates that will help you guess. If anyone comes up with a cutoff number, please let me know, and also please let me know any serial numbers and dates that you run by H&K.
Benelli M1 Super 90 M1507xx, imported 12/01/92, pre-ban
M17142x, imported 1993, pre-ban
M1978xx, imported 08/94, pre-ban
M19833x, imported 09/19/94, post-ban*
M200050, imported 09/05/94, pre-ban*
M200100, imported 09/05/94, pre-ban*
M200111, imported 09/05/94, pre-ban*
M202200, imported 09/30/94, post-ban
M205200, imported 10/04/94, post-ban
M201xxx, imported 10/26/94, post-ban
M210025, imported 01/1995, post-ban
M215900, imported 03/1995, post-ban
Benelli M3 M19199x, imported 05/14/94, pre-ban
M1967xx, imported 08/94, pre-ban
M20595x, imported 11/04/94, post-ban
*Note: Discrepancy between M19833x (9/19/94 post-ban) and three larger serial numbers M200050, M200100, and M200111 (9/05/94 pre-ban). There is no accounting for this discrepancy. All information was provided by H&K and/or Benelli. Presumably the shipments of imports did not come in perfectly ordered by serial number. Many manufacturers and/or importers are in this same situation and that is why they can't provide a "cutoff" number.