My cousin in Buffalo got married in 1991 and I was living and working in FAI at the time. It just so happened that one of the interchange routes was FAI-ANC-SEA-ORD-BUF. I was able to board in FAI and stay on the same plane all the way to the end, and vice versa.
The AA/AS interchange flights were numbered 391, 394, 395, and 396 as I recall.