It is not possible to bank CPC hours beyond your current 5-year period. For example, if you have a card that expires in September 2019 but have completed 35 hours by September 2017, you won’t be able to start your next cycle of training until after the expiry date.
On each driver’s online training account, there are validity dates listed at the top of the page. To register for access, you can enter a driver’s licence number and postcode here. A pass code is then posted out by DVSA and once this is entered along with the driving licence number, the training account should come up.