This was a data hygiene measure required for Engage users, see T91667. Donations from December and January will require the field. The intention is that we want to give donors credit for the correct tax year, which is determined by postmark date.

However, we know due to chronological forwardness that it will not be 2017 until Jan 1, so we can relax the rule temporarily to make data entry easier. Once the calendar happens, we can reinstate this requirement.