I often see the argument that they aren't the same team because of the moves at the deadline and that the +8 RD doesn't factor that in. But on July 31 they had a RD of +9. The rest of the season they played -1 ball and ended up +8.
I don't really know why that is, i.e. was someone hurt during that period, etc. But after the trade deadline they were even worse than before. I don't even know if this means anything. But it's not like they were a -40 team, made those trades, and then suddenly played like the 95 win team the rest of the season. They've struggled with run differential all season.
http://www.baseball-reference.com/games/standings.cgi?year=2016&month=7&day=31&submit=Submit+Date