But not all banks report property tax payments on the form they generate, Form 1098. Wells Fargo and Quicken Loans say they do report property tax payments on the form. And no, alas, you cannot call them up and ask them to add whatever you are paying on your own to what was already sent from the escrow account this year. They will not adjust the figure.

Apparently, though, there is no legal requirement for a bank to report property taxes paid from an escrow account at all. Bank of America and Chase do not report it. Bank of America was fulfilling requests for additional property tax payments from people who already had property tax bills in hand, but it stopped doing so on Tuesday.

Also, here’s an alert for a possible future headache: If you do prepay and have a mortgage and an escrow account, it may be a hassle (or impossible) to get the bank to adjust the original 2018 property tax payment schedule that it set on your behalf. You will want to let the bank know what you did and ask it to make whatever adjustments it can.

So people who want to prepay before Sunday but avoid trouble with the I.R.S. are faced with an interesting set of questions. If you’re sure that your jurisdiction has officially assessed taxes that you can prepay and deduct this year, but you have a mortgage with Wells Fargo or Quicken Loans, you will probably have no problem if the I.R.S. hassles you about differing amounts on different forms. But would the agency also then help itself to a look at other parts of your tax return? And have you toed the line on some of those other parts, or stepped over it?

People who have mortgages with Bank of America and Chase and may feel they are in the clear because of a lack of conflicting tax forms, even if their local taxing authority has not been precise on whether prepayments fall in line with the guidance that the I.R.S. issued this week. But beware: If your property tax deduction is much higher in 2017 than it was in 2016 without your having changed residences, that could be its own flag for some line of audit-sniffing code that the I.R.S. has written or will write in the next few weeks.