I could try to help here. But it might help Christian if you show him an example query and an example record of interest - but I think I know what query you are talking about.
An NDC code can be valid at a certain point of time. Even if it is currently invalid, meaning no one should be able to write a script with that NDC, it doesn’t mean it was always invalid. If NDC 123 was good in 2003, we want to map it to a CONCEPT_ID if we have a prescription record from 2003 with that NDC 123 on it. The relationship is valid, just the source code is no longer being used today. If our CDMs are done right, the proper concept mapping would take this into account. At Janssen the next round of CDMs will have this applied. Here is the thread where @Christian_Reich talks about that here.
@Chris_Knoll if I’m misunderstood your question let me know and @Christian_Reich please correct me if I got something wrong here!