Can't you say the same about MLB, the NBA and NHL?
All have expanded.
Why is it harder to count? Just look it up.
Now, one can argue about AFL champions counting before the merger, but one could say that about the ABA, too.
Back in 1965, before the Super Bowl, there were 14 NFL teams and 9 NBA teams. Should we discount those championships by the Celtics due to only 9 teams and a truncated playoff schedule?
I think there was like 6 or 8 NHL teams back in the mid 60's. There were 20 MLB teams.
The NFL was pretty established, as a league and had as many teams or more than the other 3 major sports leagues all the way up to the first Super Bowl.