I don't know when banks typically charge off their debt. In order to declare the debt uncollectable, for tax purposes, a taxpayer must take "reasonable steps" to collect. That's a very squishy rule, which probably favors both the bank and the debtor, because each can argue that the debt was either collectable or uncollectable, as may be necessary to support their argument against the IRS.
The 1099c shows the date that the debt was cancelled, and it further shows whether the debtor was known by the creditor to be in bankruptcy at the time of cancellation. So, the IRS probably requires proof from a debtor-taxpayer, any time that the bankruptcy box is left unchecked.
You may be overthinking this, though. If the bank has a deficiency judgment, it would ordinarily have to hold a judgment debtor exam in court to ascertain all of the debtor's assets and their location before requesting a writ of execution or garnishment from the court. And, if it doesn't, then you could argue that it failed to take reasonable steps to collect before cancelling the debt. Point being that you will be served an order to appear in court for that exam, or some other legal process intended to discover your assets before the bank cancels the debt. That's when you would be thinking hard about filing bankruptcy. And, if the bank doesn't conduct that postjudgment process, then you have an argument that the bank didn't take reasonable steps to collect, which means that the debt is not uncollectable under the IRC, and the 1099c is erroneous.