Specifically there are various bad input states which aren't detected until trying to actually populate the matches -- i.e: after the leagues have all run.

Known scenarios:

• if you add a reference to a match that doesn't exist (e.g: '500' with only three rounds)
• if you add a reference to a seed which doesn't exist (e.g: S30 with only 25 teams)
• if you put the wrong number of teams in a match

Related to this there are no warnings for omitted seed values. This will need to be a warning (perhaps via the compstate validation logic rather than input validation) as it is legitimate to miss off the bottom seeds. Likely we don't want to miss seeds from the middle of the list though.