I have a 3" rounded receiver Gold SL (the traditional looking one; vs. a semi-humpback) 12 gauge and it has speed fees AND a mag cutoff switch. Maybe some didn't, but the SL's I've seen do have the mag cut off.
Interesting, I've only seen a few of these in the wild and don't recall seeing the magazine cutoff switch on any of them. I also checked a 2006 Browning catalog and it stated this particular model did not have one. Maybe you can post a pic of that beauty for my hungry eyes. I wonder if they changed the following year or two that they were produced.