Lots of IRS regs are about the common case, not weird cases. As an analogy: if I get paid by check on december 30th, and the check doesn't clear until january

Lots of IRS regs are about the common case, not weird cases. As an analogy: if I get paid by check on december 30th, and the check doesn't clear until january 2nd, is the income for the old year, or the new year? What if I hold onto the check, waiting for the new year? How about if I have the check, but I'm snowed in, and can't get to the bank? What if I can get to the bank on december 30th, but the bank is snowed in and closed? (Answers: old year, old year, and then two don't knows)