As far as I understand, in OGS:
- “The final score of the game”, outside of estimator, is correct, there is not bug around it luckily, and you can pretty much trust the final result as being right (assuming that dead stones and such are correctly marked by players at the end of the game).
- The score estimator is just an estimate, and has always been fairly unreliable. I recommend that you try getting used to never using it, as it feels more like playing on a real go board, but that is just a matter of preference. It is important to understand though, that estimator is just an estimate, and can be and often is wrong.
- The estimator always uses Chinese Rules, no matter the actual rules used in the game (Computer-simulation techniques are generally easier to implement in chinese-like rules). This can be a further source of confusion.
- The estimator has (had? I think it was not fixed, but I might be wrong) an important easy to fix bug for handicap games, because it does not correctly take into account the handicap stones in chinese score (it is customary to subtract N-1 points to black’s score in handicap games when counting chinese, because black starts with “one additional point per extra stone” in the beginning, so subtracting them makes the “amount of handicap” equivalent both when playing chinese or japanese). That means that, in an N stone handicap game, it is off by about N points, even at the very end of the game. We discovered that during a game in the Argentine online league. A more detailed explanation is here Score estimator is very wrong in handicap games, and also very easy to fix