There have been some reported issues with the file is rebuilt warning.
The 1970 date is just a null value - meaning it cannot find the timestamp for the references in the assembly file being checked in. Opening and saving in SW usually fixes it.
I've been having this problem too. I recently began using EPDM from another system due to position change and thought this might have been a quirk with newly registered files for some reason. But the list below are files that have at least 2 versions, some even have over 12. I have found NO WAY to rebuild deep enough to get this message to disappear forever. I have gone down to the part level, done the "Rebuild All Configurations" trick, CTRL+Q, CTRL+B, etc.
Anyone else seeing what Kevin and I are seeing on EPDM 2010 SP2.0??