Beside the full import functionality, M2IF also supports delta import functionality. The delta import supports SKUs for
that are NOT part of one of the actual CSV files.
In contrast to a full import, which requires the following invocation of the appropriate indexers, after a delta import the delta indexing functionality takes care for the necessary index updates. The delta indexer can not be started on the commandline, instead it'll be started by the default Magento CRON job.