I just read the article through for the first time, and I see the note you referenced (the footnote on pp. 24). I also see what other posters mean when they wrote that the WTB&TS is making two contradictory assertions almost within the same paragraph. Mainly, that the business documents may show an overlap of kings. They do this in order to try and cast doubt that the business tablets are a valid source of information regarding this period. Yet, the footnote you cite shows that unless there are gaps between the kings, 607 becomes unfeasible.
Also, I don't know if any of the other posters mentioned this in the previous thread, but the content of the tablets also matters. The same business deals, contracts, families are mentioned in them, allowing the documents to become interlocking joints between kings. There is no way to find 20 years between these kings, and there definitely is no way to find 20 years if one's argument is that the kings reigns overlap.
(Note: the are getting "overlap" happy these days, applying it to everything!)