Yes, cohort definitions give you the option to search by source_concept_id. It’s one of the options when adding criteria attributes to the domain criteria. For example, Condition Occurrence shows a ‘Add Condition Source Concept’ as an option. That will allow you to specify a concept set containing non-standard concept IDs. You can leave the main condition criteria to be ‘Any Condition’ and it will only look for the source concepts you specify. If you specify both standard and source-concept attributes, then the criteria will look for both the domain concept ID AND the source_concept_id to be found for the given record.