JS_Harris - 11:20 am on Aug 13, 2013 (gmt 0)
An interesting observation: These pages were published years ago but when I set the 'search tools' option on Google search pages to 'past year' these pages show up in results again. I'd say that definitively means Google updated the publish date as I updated the content and I now have a STRONG suspicion that this has devalued the old incoming links for these pages.
A link today is a vote for the page today. If you update the page tomorrow then yesterdays links are no longer as strong a vote for the 'new' content. It's the only thing that makes sense right now. I've changed templates and other parts of pages before without problem so this would seem to apply only to the actual content.