Single Status Update
About NASCAR Days of Thunder's sponsorship trophy, I got the trophy before completing the final race (30 laps at Talladega) - after taking pole on all races, instead of completing the last race at Talladega, I've re-runned Martinsville (I was also racking up takedowns - at that moment, there were lefting for me "takedown 100 cars" for a sponsor, and "pole all tracks/races" for another sponsor), and the trophy popped (I'm not sure if it was soon after ended the race or when I've checked all unlocked sponsors...). Maybe you must unlock all sponsors (and get the trophy) before actually finish the season.
I hope my info helps you. You can send me a message if there still are some doubts.