My husband became a resident in Canada Dec 23, 2016. Should I say on his return that his residency changed in 2017? He was not here in 2016 and therefor did not do taxes

Generally, where you lived on the last day of the tax year determines what credits you're entitled to.

If you moved during the tax year or since, it's still where you lived on December 31st 2017 (or the last place you lived in Canada during the tax year) that will decide what applied to you. If you indicate a change of province/territory or residency that occurs in a year that is before the taxation year, you will likely get a NETFILE error.