Jean et al
I think you have to keep in mind we are talking about a "Worksheet" and not a kantei-sho, it is not set in stone until they issue a paper. The team kantei's the sword and then based on the work if mumei they assign an attribution. In the case of unique workmanship making that assignment is easy. However some swords will be harder than others to peg depending on many factors. If they decide upon a particular era in their assessment, as they should, they then must consider the schools active at the time that might have produced the work. Just as you would in your kantei. So on this work sheet they may have noted Eisho koro as the time when they felt the sword was produced. And just as you would move on to the maker. Once they decided upon a maker they may not have pulled the dates from the Meikan. No one can be expected to have memorized all the eras and so it could be the Eisho koro comes from memory, maybe a little early but still within a generation of Tenbun. Had they said Eiroku then it is neither Tenbun nor Genki so what would we make of that? I think they are seeing this sword as early.
Still the most important point is this is a "worksheet" - once they return to Japan they check all details of the swords that were recorded and will revisit the Meikan before they issue the certificate. I feel certain if they do not give it to a certain generation they will place it in a time frame that lets the owner do that. I am curious to see if this does not turn out to be the case.
-t