Number Number, Who's Got the #
Most if not all builders will put the hull # (aka the "one design" number) on the main and any overlapping sails. This makes boat identifyable for local club racing. If in distress, it will greatly help the SAR folks more quickly ID you if there are other sail boats in the vicinity (well, besides you shooting up flares!).
So, if the hull number, from your HIN code on the transom, is, say 1238, you would have hull #1238 that was molded out for that model.
Unless the mfgr was really cheap, they would always put that individual hull # on your sails. Sometimes the first buyer is saving every possible nickel and opts to have blank sails.
If you, being a later owner, want more info on your exact hull #, you could just contact MacGragor and give them the HIN on the hull and verify that number. Lucky you! Your builder is still in business!
Fair winds,
LB