Might also be interesting to see if mentioning a target ELO score actually works over enough simulated games. I can imagine there might be regular mentions of a player's ELO score near their match history in the training data.

That way you're trying to emulate cases where someone is trying, but isn't very good yet, versus trying to emulate cases where someone is clearly and intentionally losing which is going to be orders of magnitude less common in the training data. (And I also would bet "losing" is also a vector/token too closely tied to ANY losing game, but those players were still putting up a fight to try and win the game. Could still drift towards some good moves!)