Seniors and students

Yes, if CRA has that information in their files as "unused contributions" you can trust it and claim the deduction on your return.

This happens quite often if you missed claiming a deduction years ago. Because CRA gets a copy of the RRSP Contributions slips as well, they will often add the slip when you use the AutoFill service. You can always go look at your RRSP Contibutions made and pinpoint where this one(or more) is coming from. Do so using your CRA My Account.