I don't think there's an expectation that a skill rating is comparable throughout 20 years, because both individual players and how the game is played (the meta) changes continuously.
But if that's true, then why would rating inflation be a problem?
But if that's true, then why would rating inflation be a problem?
In some sense, it is not surprising that we do not have a system that accomplishes this. Since it is impossible to see the results of a game between players living in different time periods, we cannot get any data to prevent drift. You can still try to normalize the rankings. However, unless you have some independent way of measuring skill, you would need to make an assumption about the relative strength of players. Assuming the average skill of a proffesional is constant across time is probably not accurate, but closer to reality than what you get with unchecked inflation.
Of course, scores will only be comparable if the average skill of all players remain constant. I would imagine this isn't true, but the drift over several decades is probably small.
Unless you start introducing some purely objective criteria for skill, which can never work, this is the best you can do. It's still way way better than a straight elo system though.
[0] https://chess.stackexchange.com/questions/2550/whats-the-ave...
1. Assume that chess ability is normally distributed in the population.
2. Assume that people who are terrible at chess are more likely to stop playing chess than people who are successful.
Then you've sampled the underlying normal distribution mostly from the top end, and that new, highly skewed distribution is what you'll see when you measure everyone's rating.
It would be very difficult to account for these factors in a way that keeps comparisons across 30-year+ time spans meaningful.