Given the size of the club-player database in SMS2 it is impossible to keep it entirely up to date, many of the sources used do not appear until 2 or 3 months into the season, and do not contain all the necessary facts.
The English data is approximately updated to the transfer deadline of the 95-96 season. This data is the most accurate in the game, ages and full names are correct. Positions and skill levels are based on my own opinion or are estimates.
The English non-league data is very much guess work, ages and first names are made up.
Of the European data, the full names are correct but many of the ages are made up.
The full version of SMS2 includes a data editor which allows the user to modify all club and player attributes, as well as past cup winners and current cup entries. It is also possible to swap clubs between divisions, so a 'Super League' can be created.
The data editor will let users of the registered version of SMS2 correct my errors in setting club and player attributes. They will also be able to cheat by modifying the player skills or club details for the club they intend to manage.