The defendant has to prove their own affirmative defenses. Does the defendant have evidence that shows the last date of payment?
The plaintiff also has to prove their allegations.
It's very possible that a person has 2 or more bank accounts,
If the defendant has more than one bank account, he could present evidence from a 2nd bank account, as well. But if he doesn't or didn't have a 2nd bank account, he can't prove what never existed. He denies it in his affidavit.
just the bank statements alone would not be enough IMO unless the defendant has been using the same bank account to make payments every month.
If the judge felt it was necessary, the defendant would provide enough copies of bank statements to show that he made payments on a regular basis from that one account which would also show a payment on the date he claims is the last payment.
The point is that if the defendant presents credible evidence that he did not make the last payment, the plaintiff would have to do more than speculate as to how a payment could have been made.
In the OP's case, if a JDB were to claim that a last payment was within the SOL, it would seem they would either have no evidence, or they'd have to create a fake document.