Retirement tax questions

Thank you, this was helpful.

I actually have a few payments to consider, and the postmarks range over the last couple weeks of the year. Our checks come to our PO Box, and some things piled up at the post office over the Christmas Holiday. We went to the PO Box after December ended.

So with no way of knowing for sure when it arrived at the post office box, would you recommend making an assumption of the arrival date based on the postmark, or would it be safe to simply state that we didn't receive the payments until the year changed? The amounts are substantial enough that they will impact our account, and I would prefer to post the payments in 2016, but only if it is safe to do of course.

Thanks again.