Thank you for putting this plainly, because few vendors have noticed the difference.
On your first point, I do not think you are wrong. There are two tests, and a preferential certification answers only the preferential one.
On what to ask instead, may I suggest a short signed statement from the vendor: the country the goods may be marked as, where they were actually manufactured, and for assembled items where the last real production step took place. Ask for it per part number, and keep it on file.
A parallel, not your law: our preferential rules here hold the importer responsible for origin information even with a certificate in hand, so the certificate alone was never a shield at my desk.
I hope your September files pass quietly.
Ran your three. Marking country: signed, no argument. Place of manufacture: slower. Last production step on assemblies: nobody signs it. CBSA has not moved.
Bev, your third line is the answer: that step is not coming. A plant that refuses it today refuses it later, and your truck is at the gate now.
So file the line as it reads without the vendor: caught, surtax paid, freight moves. The importer goes back for the money afterwards, and that road wants the same statement, so the gap sits with their buyer, not with me.
Not a letter from the importer. My licence lost its excuse for someone else's data. The file as I sign the pedimento is the only defence left, and a letter is not a production step.