If the AS is uninstalled and reinstalled for whatever reason, and there is a good backup of the previous state we can restore it. This will result in some data loss for the period between the backup and the last operational time of the AS. But once the restore is performed on the AS, this should put the cflist data back on the AS which contains the info about the existing DS (We are assuming here that the device servers have not been touched). In this case after the AS restore, things should work normally and there won't be any mismatch in the AS/DS data other than the data loss as explained above. This will resolve the DS registration issues.
If a device server fails, we have to reinstall that device server, but we would then have duplication in the database because of the registration process. In this case there will be a duplicate entry in cflist as a new popID will be created so that should be manually deleted. This problem has been taken care of in 9.2.
If there is no backup available, it is recommended that a full reinstall for both the AS and DS be performed