Why do they include 2017. And 2015 for that matter?
The intent is to then be able to say there were x-thousand Russian ads influencing the election. The reality, when one actually looks at these sad little "ads" is these Russians were just churning out click-bait that had nothing to do with the election at all.
One could find any number of companies in the world churning out silly click-bait ads (5 foods to avoid!!!), but Mueller needed to find "Russians" churning out ads during the election cycle to then label them as political ads, when the ads themselves are just junk ads about nothing.