Perhaps they are comparing the previous approved applications with the pending 485 application for consistency? If there was a major deviation, can it be accounted for by a valid reason?
Things that come to mind are:
skillset, wage determinations, paystub/W2, work location, employers etc.
Also, they might be interested in any special annotations made in the previous applications while they were being processed.
I believe it is a good thing in general if any of your applications (pending/approved) have been touched. Better for someone to be looking at your application rather than it sitting in a corner gathering dust.