When a service bulletin is revised, it is often required for the engine to be complied to the new revision number.  If you find that an engine that has already been complied changes to Not Complied, it most likely is due to the issuance of a new revision.  The compliance summary always lists the compliance data for the latest revision number of the Service Bulletin.  To see the compliance data entered for the previous revisions, click on the revision number next to the engine serial number to bring up the Compliance History screen.