When I say "raw", what I'm referring to is the preservation of the data's chain of custody. If I'm looking at the data with an intent to sue the respective government agency, then I have strong legal reasons to make sure that the data isn't modified. If I start from open data for example, the gov agency will have their data person sign an affidavit making this very clear and I will lose my case basically immediately.

  The issue imo is that a person closer to the point the data was collected or merged is probably better equipped with understanding of what may be wrong with it

You'd think so, but just like most other systems, systems are often inherited or not thought out, so the understanding is external and we can't assume expertise within.