Robert_Charlton - 9:38 am on Dec 2, 2013 (gmt 0)
Both the resurfacing of old 404s, and spurts of non-converting foreign traffic (also known as "zombie" traffic), are signs of various types of Google updates... and, IMO, of Google testing.
We're still not quite sure what the zombie traffic is, but I'm looking to compare notes in this discussion...
Seeing some big traffic dips with no ranking changes
I've included in the thread some notes and links to explain the 404 issues, which those concerned about them might find helpful.