Thanks, MLHmptn. I realize that the EMD Update was during the overlap period with Panda, and that can make analysis really difficult.
The bulk of Panda Update (and it was a true update, not just a Data Refresh) rolled out on Sept 27, but some of it - and I sure wish we knew which parts! - did take 3-4 more days.
The EMD Update was announced the next day, on Sept 28 in the afternoon Pacific time. So it is possible that the first definitive traffic change from the EMD Update you can see might be Sept 29.
I hope you can sort it out and let us know. For sure if you saw the drop on the 27th, that was Panda.