Too often, prosecutors do not obtain official MTO documents to prove status charges like yours, instead relying on what the officer testifies. But, some courts view that as hearsay. After all, if the prosecution wants to rely on MTO status, then they can simply provide certified MTO documents. The officer telling the court what they read on their computer system in their vehicle is no different then if they were to tell the court what they read on the internet.
So, while you have an excellent case on the seatbelt offense, you don't want to give the prosecution too much opportunity to gather the MTO document. They might not have requested those before court, assuming you would be pleading on a deal.
By the way, I probably wouldn't even take the stand in your case. That way you won't have to answer when you last paid for a plate renewal. In other words, don't give them an opportunity for you to hang your own self.