my understanding is that if you leave the "DATE" section blank, and press validate, it will still validate and generate barcodes. meaning the date is not important in generating barcodes.Personally, I think once a specific form requires barcodes then best everything needs to be typed, unless the specific space does not allow for typing. Eg. Date section does not allow for typing. I feel the barcode is what is scanned for records as it captures all typed information.
As for the date, provided it hasn't yet been submitted to IRCC it is only a future date for you should be fine, meaning ircc has no idea of when you filled or printed the docs. But if you mean a future date for ircc then I dnt think that's advisable.
furthermore, after validating, they specifically said to sign and date the application, meaning you can actually write dates using a pen.