Ah, @OHDSI_User, I think I might understand what you are seeing.
First, let me invite you to the EHR WG held every other Friday from 10am to 11am EST. Our next meeting is this Friday, September 20th. We discuss all things EHR & more. The meeting details are also located here. If you give me your email address, I can send you the calendar invite.
This is how it works from a clinical workflow perspective. The Person Visits a Provider at a Care Site (all OMOP language). The Provider records the ICD9CM code (if the visit was before Oct. 1, 2015) or ICD10CM code (if the Visit was on Oct. 1, 2015 to the present) - note, some EHRs recorded an ICD9CM AND an ICD10CM code during the transition from 9 to 10. This code represents why the Person had a Visit that is recorded in the patient encounter diagnosis table. The reason may be for a routine medical examination or because of a car accident, doesn’t matter if it is a Procedure/Condition/Measurement/Observation/etc., this is how it is recorded at the source.
The domain_id signifies where the data should live in the OMOP CDM. If the Visit was before Oct. 1, 2015, v70.0 has domain_id = Condition then you need to ETL it to the Condition table. If the Visit was on or after Oct. 1, 2015, then the domain_id = Procedure and the data ETLs to the Procedure table.
I highly recommend you watch the CDM/Vocabulary tutorial and the ETL tutorial found here. These tutorials will give you the foundation for the CDM and explains the model very well.