I received another slip after I filed my personal tax return. Should I keep for next year?

If we have prepared your personal tax return, then any slips received after it was filed should be brought in immediately for us to examine. An adjustment to the tax return may be required, and it is important to do so at the earliest possible opportunity, to avoid the excessively punitive penalties that CRA imposes on taxpayers who do not report tax slips correctly. Definitely do not wait until next year, by then CRA will have identified that there was a slip missed and they will reassess the return, with penalties.