As far as I interpret you issue description most of your messages are no issues. So nothing to resolve: if an employee really was assigned to cost centre XYZ in, say, 2009, and this is now closed for posting, what do you want to change? Rhinte will not change anything, as long as there is consistency between IT0001 and OM.
If you haven't checked for years, I'm sure there are some real integration issues as well, but cost centres not open for posting in the past are ok, if it's still historically the correct cost centre
Kind regards
Sven