We have found that many historic games (especially from the 19th century) are wrong in databases. Some of our corrections are minor but several involve radical corrections to the accepted scores of games.
Since 2020 we have been using Thomas Niessen's Chess Suite software, which compares PGN databases and identifies previously unnoticed discrepancies in records of the same game. (The Chess Suite has other features but this is the only one I have used.)
The software produces a report on the databases compared. Then we check these findings against the primary printed sources, although sometimes they disagree about how games really went, which requires more research and sometimes the exercise of judgment to decide between alternatives.
We found many problems with Steinitz games several years ago but by no means all were detected. Niessen's software became invaluable when preparing the final text of Steinitz in London. In the last few months we have been using the Chess Suite to detect many problems in later Steinitz games that fall outside the scope of our book.
We have now started a series of articles where many of our findings will be published for the first time.
We began with an article about problems in several games between the first two world champions, William Steinitz and Emanuel Lasker. We are sure readers must agree that it is particularly important to correct the record of their many encounters.
Our second article deals with more games from Steinitz's later career, especially his matches with Chigorin, Gunsberg, and Schiffers.
Further articles will deal with corrections for J. H. Blackburne's games and perhaps others.
Article 1: Steinitz v Lasker (introduction)
Article 2: Steinitz v Gunsberg and others
Our general conclusion is that database users, especially chess historians, need to be wary of trusting the databases. They should go back to primary sources whenever possible before publishing old games in books and magazine articles. Moreover, those who edit, post or sell databases must reform their procedures.
The main databases we have compared are ChessBase (various editions), chessgames.com (where readers contribute games and sometimes corrections) and, in the case of Steinitz, Sid Pickard's database on his CD The Collected Works of Wilhelm Steinitz. When we found discrepancies in versions of a game, we usually checked some other databases also.