MQM's for a while (not sure how far back, in your case) were the measure for Million Miler status. As long as you were crediting to Delta SM, you were earning MQM's and therefore accumulating MM.
Per the terms online (https://www.delta.com/us/en/skymiles...rline-partners) flights flown with partners will also credit to MM status. Of course, you will have to credit reward earnings to SkyMiles.