Debian packages that have been removed (rc) still show up in inventory.
Running strace on the ocsinventory-agent it shows that the software inventory collection is done using the command stat (e.g. "stat("/var/lib/dpkg/info/exim4-base.list", {st_mode=S_IFREG|0644, st_size=155, ...}) = 0" ) which catches software installed as well as removed, but not purged from a system.
I consider this a bug as it shouldn't inventory removed packages.