facts incorporate time
Think about how we structure data for ourselves (programmers): every piece of data has a timestamp incorporated into it (e.g. every log statement, every code stored in source control, every version of the database). Imagine if you had to make decisions based only on the current state of any system/data - it would be terrible! Give your programs and your users the truth - facts complete with the time at which they are true, and a history of facts.