OK nobody is talking about this but this is a BIG issue for anyone who runs amateur leagues in customs. Client match history only goes 20 games back and the web match history is currently the ONLY way for you to pull history for your own customs. opgg does not work for this as the riot Api doesn't support pulling custom games for a player
We're also looking into solutions that will allow players to query for their own private custom games with OAuth tokens through the Riot Games API. These are tokens unique to a player which allow us to ensure a player is looking up their own match history. This solution is something we're looking into but wasn't a requirement for deprecating web match history. In the interim, the tournament code solution is what should be used to create public custom games.