GABIL, I am sorry to disagree. The certificate of deposit (Which could be a letter to investor) is enough proof. The letter always contain among other things: Date of Investement, Date of maturity, Principal Amount, Duration of Investment and Interest rate.
However, make sure that the innvestment tallies with the statement you sent before. That is, if you already advised CIC on Jan 2010 that you got N1m, and it is now showing 600k as of Jun 2010, then the investment must have started in June/July 2010. With that you are safe GBAM! ;D you may even have all your POF in Fixed Deposit form afterall it is in a liquid form. Mind you, the investment should be in a short term maturity o.
when i sent my appication, i attached an FD cert. as my POF. Well is just a suggestion