What @MPhilofsky is referring to is when we create an OMOP database we don't pool different sources. We keep them separate. Unless we pool, and then we treat them as one source. To pool, and then to keep it separate at the same time, has been discussed and dismissed before. But it keeps coming back.
@MPhilofsky: Make a proposal to V6. Figure out a way to flag each record without creating a gigantic bureaucracy. Also, try figuring out what you do if you merge data from sources, like DRUG_ERA or VISIT records for the same patient.
If you feel like that is too much of it (which would be my feeling) you can still use VISIT and/or CARE_SITE and then keep an external reference table which tells you which one is which. Seems easier to me.