" Best if Used By" dates are just the date that the company can no longer guarantee potency. I don' t think the creatine suddenly went bad at midnight Dec.31st.
However, as best I know creatine has a shelf life of 3 years. So that creatine may have been manufactured in 1998-1999. That kind of puts your question in a new light.
If you' ve never use creatine though, I probably wouldn' t, you' d have nothing to compare it to to officially know if it works or not.
Besides.. Creatine is so cheap. Just get a new kilo. It' s not expensive and why waste your time on stuff that might have gone bad?