flanok - 10:26 am on Dec 4, 2013 (gmt 0)
I agree with your opinion about old pages that should be 404's, now being re-used amd creating Panda issues. (i think this is what you meant).
I have just created a sitmap for WMT with 59 old pages that have not existed for at least 9 months (that now have replacement pages in different directory).
The sitemap now lies in WMT with 0 pages indexed (as it should), but interestingly NO errors also.
These are 404 pages, why no errors? Unless, somewhere in the Google system it is not recognising these as 404s.