I think that everything is OK
You want to check Sessions in the Internal Database context to see if there may be some old ones that backed up the machines that you are referring to, and most important, to see if they are still protected
It is a common mistake, especially with those just starting to use the product, not to realize the default protection is set to Permanent. As long as a session is protected, the filenames associated with it will not be purged, and the hostnames associated with those protected files will not disappear when you do a 'writedb/readdb'
In the short term, you probably have nothing to worry about. Longer term, every once in a while, check older sessions to see if they are protected. If the are, obtain the media label, export the media, this will remove the session from the IDB, and, when you do the next writedb/readdb, those hostnames will disappear
The 'writedb/readdb' should be considered a maintenance item, and, in my opinion, should be done about once every 6 months