it must be an unwritten rule
I don't remember it ever happening
I think there is a practical reason.
Lets say, per your example above that UNL suddenly had an opening on 9/7/2024. And, for the sake of argument let's further stipulate that USM, Marshall, or WMU backed out of their game against tOSU such that the Buckeyes actually also had an opening on the same date.
Now, per your example, the UNL AD calls up the tOSU AD and says "Hey, let's play a non-conference game on September 7, 2024."
If I'm the tOSU AD my answer is "Sounds great, do you need any help with travel arrangements to get HERE to COLUMBUS for the game?"
Therein lies problem #1. The Huskers and Buckeyes are both missing a home game. If they are going to play each other then either Memorial Stadium or the 'Shoe has to sit empty on that date.
The compromise would likely be a H&H but that means playing not one but two non-conference games. Why? As an Ohio State fan I'd rather have my marquee OOC games be against teams we rarely play, not conferencemates that are off schedule.
