Hi @TMS,
This question is best asked on the CDM Builders forum . This thread is about EHR WG related activities, so your question is likely to be overlooked.
But the short answer, you should map based on the vocabulary_id of your source data. If you have a LOINC code, join to the CONCEPT.concept_code WHERE vocabulary_id = ‘LOINC’.
I have a feeling I’m not fully answering your question. If I’m not, post it to the CDM Builders forum with a little more background. And we can figure it out.