This is YTD comparison chart. In this chart we want to show the check box selected on filter only on completion of month. For Example November 2018 is going on then we will show the by default check box selected till October but data 2017 will be calculated till October only. Filter should show January to December but tick or selected only on from January to October.
Data of November is partial in data base thats why we don't want to show partial only complete month data will display on base of filter.
When I am selecting 2017 and 2016 then complete month from January to December for both the years will display in the filter.
I would check out this KB article on showing YTD data while excluding the current month. In this case it would be the month of November or now given this post is old. The month of December from the YTD data.