It is unclear from the documentation if this is a directory (as in the RES) or if this includes the files as well.
This is further complicated by the CSET_FILE_NAME_METADATA_PATTERN under CSET_INCREMENTAL_DATA_FETCH
This may be something that will become clearer when multiple dates can be added as I imagine it will use the naming conventions that people are used to when cycling over different forecast cycles.
What problem does your feature request solve?
CSET_FILE_NAME_METADATA_PATTERNunderCSET_INCREMENTAL_DATA_FETCH