I had the same issue...you chose the Raiders...for some reason their 2020 move to Vegas is hard coded...the way around it is this...
Start new league ( I too used that 83 start)
I to used the 83 start...the glory years.
When you begin, under the new game options at the start, choose the option for level economic playing field...this undoes that hard coded 2020 move to Vegas and allows your team performance on field to determine attendance. Without that, those fickle Raider fans punish you for 40 years for that future move lol