First, thanks to anyone who may have taken the time to view this post.
The issue is resolved. I determined that I needed to use Year([Approval Complete Date]) as [Approval Completed Year] in my Load Script as opposed to any of the other three options I listed in my original post. That gives me just the Year value and no duplicates, for example, in my straight table when I click the filter arrow for the Approval Completed Year column (I only get 3 choices, 2016, 2017 and 2018 and not two 2016 , 12 2017 and two 2018 choices).
Additionally, I had the same problem with formatting the date as YYYYMM. To solve that problem, I used Date(MonthStart([Approval Complete Date]), 'YYYYMM') as [Approval Completed YearMonth] in my Load script as well.
If anyone should have any comments or feedback, please let me know. Thanks.