I puzzled over the role of the 'National Archives' and finally left it out, since I had a difficult time justifying it.
Two difficulties with this record:
1. The role of Ross Spencer. I decided in the end that he could only be considered a third author, as there was no relationship designator to describe his role as an additional contributor.
2. The role of the National Archives. Again, I had trouble finding a relationship designator which accurately described its role in the publication.