I received this message from my score watch today telling me my score dropped:
You moved from one category of credit users to another as time passed. For example, you may have transitioned from the category "consumers with a new credit history" to the category "consumers with a two- to five-year credit history". As a result, your credit report is evaluated differently, causing a slight change in your score. The good news is that moving between categories like this usually offers you the potential to reach a higher FICO score in the future.