An incorrect birth date is not a fatal error. Your best option is therefore to set it down for trial and then on the trial date either hope the officer doesn't attend (whereby it should get withdrawn) or take a reduced fine offer by the prosecutor. That offence is a black-and-white one (there's no grey area). Your sticker was either expired or it wasn't. If you've got no proof of renewing it before expiry, then you'll really have no defence.