Ideas for next time:
All matches start/end at the same time. Designated backup host(s) w/coordination to avoid gaps/mishaps. I'm not sure what the deal was this year but I found match start times extremely unpredictable and often delayed -- having a helper could have fixed most of this.
For auditability, there should be a complete record of all votes in an authoritative source. At a glance, I noticed some match tallies posted on the bracket site differed from the board vote totals, I'm guessing due to some kind of out-of-band voting procedure. All users should be able to see whether they voted in a particular match and who they voted for. An admin should be able to see the full result in case any questions come up. Ineligible votes should be filtered with a system in place rather than guesswork.
Real results posted with breakdowns (not just a video, definitely not text inside images). It would be basically impossible to recreate the official results for every match just from the data currently in the forum (polls + results posts). You can only go back and discover something 10 years later if the data was laid out in the first place.
Host doesn't run his own matches.
Can't vote in your own match. Or if this is really desired for some reason, it should be crystal clear from the outset that it is allowed.
Vote of the day is 1 or possibly 2 hand-picked votes rather than just a splat image of them all. Also don't reveal who they voted for since some VotDs are easy to pin to a user on writing style or content.
Bring back spreads! Over like Grover!
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Also someone eventually needs to do the work to integrate this contest with our super awesome full historical record of all past Summer Contest matches, here:
https://contest.the-elite.net/If you want to volunteer, shout it out! It's a bit sad we didn't use the Vote Machine this year, it would have taken care of most of the points I made above.