BP, do you still need these measurements?
If you are feeling frisky why not? It would be interesting to pin down when the change occured, but I'm not going to lose any sleep if you don't feel like it.
As the quote above from Ask Audyssey shows, Chris was saying that it was there in March 2011, and now he says that it disappeared "several years" ago. So the 4311 could have been right on the cusp of the change depending on how accurate this inferred chronology is.