Hi Phil,
Sorry for being late to reply.
You can easily differentiate that with the category. Use a new category for the ones you want to hide. In the category slug(see below), just don’t use that category. Just create a shortcode like below:
[wpdm_category id="Category Slug or Slugs" operator="IN" title="Custom Title Here or 1" desc="Custom Description or 1" toolbar="1" paging="1" order_by="field name" order="asc or desc" items_per_page="10" template="template name or ID" cols=4 colspad=2 colsphone=1]
Hopefully, this will solve your issue.
Cheers
Salahuddin Ahmed