CRA acknowledges that it has discretion to waive its requirement for a vendor GST/HST registration number that is valid on the supply due date

CRA considers that in order for a supplier invoice to be a good invoice for input tax credit purposes of the recipient, the quoted registration number must be valid on the due date (or, in some circumstances, payment date) for the supply - except that CRA acknowledges that it has the discretion under ETA s. 169(5) to waive non-compliance by invoices where it is satisfied that there is or will be sufficient information evidencing the particulars of the supply and the tax payable.

Neal Armstrong. Summary of 8 March 2018 CBA Commodity Tax Roundtable, Q.15 under Input Tax Credit Information (GST/HST) Regulations, s. 3(b)(i).