WGT have never publicly revealed the criteria for tiering up via coin rooms. I don’t think it would be as simple as playing X number of games at, say, Legend in order to tier up to TL. There would have to be some sort of win ratio attached to it otherwise you might play 500 games as a Legend, lose all of them and then tier up to TL and that’s obviously not desirable.
My personal theory is that yes there is a minimum threshold of games played, let’s say 500 to keep it consistent with the Ranked Round algorithm, but instead of lowering your average you have to maintain a win ratio of say 80% against other Legends and say 20% against TL and above. There would have to be some way of demonstrating that you’re in the upper echelon of Legends and deserving of tiering up and tracking win ratios against your level and above is the only practical way I can think of doing it.
This is pure speculation on my part though so I’d be interested in hearing other people’s opinions. Or maybe something from WGT?