CIC explicitly asks for minimum 4 months bank statement for this exact reason, to make sure you have the money for the duration and wasn't credited last minute. Most people get their bank statements stamped and signed by the bank staff/manager, this shows CIC that they are authentic statements. If they feel that documents may be unauthentic or that you didn't provide proof of funds throughout the 4 month period they would never go out of their way and go verify with the bank, they would just refuse the application.