I just wrote about two 3.5 teams from Seattle that played each other three times in the same season; sub-flight, local playoffs, and Sectionals. It turns out, it is very common! At least this year it was, as another two teams from the Seattle area played each other three times.
These two teams were in the 4.5+ teams in the 40 & over division, Central Park and Amy Yee.
They were both in the same sub-flight in local league play where Amy Yee won 4-1 and won the sub-flight.
Both teams advanced to local playoffs where they met in the final, Amy Yee winning again 4-1. But again, a wildcard allowed both teams to advance to Sectionals.
The teams were in different flights, but both won them going undefeated setting up the third match-up of the year. Central Park did improve, but still lost 3-2 sending Amy Yee on to Nationals.