The OR will look at the last 6-12 months of your financial history as a matter of course. If there are things that don't add up (i.e. you try to hide things from the OR by saying one thing but your statements show another) then they will look back even further.
Most people are asked for the last 12 months of CC and bank statements but this can vary from OR to OR. If you don't have the statements then the OR can easily get them from the bank or creditor.