mdotk - 4:05 am on May 18, 2013 (gmt 0)
Guys still reviewing all your comments - many thanks!
To confirm, looking at Analytics it is very clear that I was hit on 27 Sept-1 Oct 2012.
Exact-Match Domain (EMD) Update — September 27, 2012
Google announced a change in the way it was handling exact-match domains (EMDs). This led to large-scale devaluation, reducing the presence of EMDs in the MozCast data set by over 10%. Official word is that this change impacted 0.6% of queries (by volume).
Panda #20 — September 27, 2012
Overlapping the EMD update, a fairly major Panda update (algo + data) rolled out, officially affecting 2.4% of queries. As the 3.X series was getting odd, industry sources opted to start naming Panda updates in order (this was the 20th).