That is fine but don't later ask why the system has 10 different customers for Commers Ltd I ended up building another table and logic just to do roll-ups and

That is fine but don't later ask why the system has 10 different customers for Commers Ltd I ended up building another table and logic just to do roll-ups and account for name variations. But I told the client that they really need to invest in a serious cross-referencing middleware that tracks identities across all these systems and uses ID numbers to coordinate all the legacy systems. But yes trying to develop models or even simple aggregations that rely on this kind of data can be quite frustrating.