could be in the other division and VT doesn't play either school in a season. If you look at the other conferences with divisions, then they are pretty much using the same rotation pattern as the ACC. The MAC was kinda quirky because it had 13 members, so teams couldn't always play a round robin division schedule. The Big Ten will run into schedule quirks because Indiana-Purdue is the only protected cross-division game. The Pac-12 has its own quirk because the Cali schools are the only ones with protected games (2). For the most part, the ACC's rotation follows this pattern:

Year 1: @A1 and A2
Year 2: A1 and @A3
Year 3: @A1 and A4
Year 4: A1 and @A5
Year 5: @A1 and A6
Year 6: A1 and @A7
Year 7: reverse of Year 1
Year 8: reverse of Year 2
Year 9: reverse of Year 3
Year 10: reverse of Year 4
Year 11: reverse of Year 5
Year 12: reverse of Year 6

Expansion or schools leaving the conference can force a conference to reset the rotation pattern or even create a new rotation pattern.