Here is an excerpt from a post in the forums over at MariusNet:
One of the things the MCS does is 'age' games. Games played in the last 7 days are worth 100%. Games 8 days old are worth (100 -8)/100 or .92 (or 92%) of full value. Games 20 days old are worth (100 - 20)/100 or .80 (or 80%) of full value, and so on. Meaning a game played 90 days ago will be worth only 10% of full value. This aging process means there is never a need for a reset. All games will eventually age out of the report.