[Design of Marci Letter]

[asteckley]

I hadn't realized it before, but the tab at the left has small pinpricks, several of which seem to allign quite neatly with the sewing stations of the inner front cover, suggesting that the letter may have originally been sewn to the front hinge of the manuscript (in blue below).
...
I don't think there is any evidence of paste on the letter...it's paper, so adhesive would have left significant damage. It's fairly easy to remove adhesive from parchment, but paper is much more delicate.

AND

About Andrew's suggestion that the small fold might have been a glued "tab": This caused me to look more closely at Lisa's light table image of the Marci Letter, and lo and behold there is something there... some irregular deposit:

I don’t think the holes are from binding thread—I think they result from fatigue and wear, for the reasons I described in the paper. They may also have been worsened at points by direct contact with structural elements beneath the tab, such as the binding threads or sewing stations.

Lisa, I know when I first pointed out the binding tab to you, you suggested looking for regularly spaced slits along that crease. The reason I didn’t go that route is that I just couldn’t see regular spacing in those holes along that crease. And because they look exactly like what one sees with fatiguing (i.e. repeated folding/unfolding) along a single fold line.

That said, I do agree that if the tab had been glued, we should probably see more visible damage from its removal. However, if it were attached using a starch-based paste (rather than a protein- or animal-based glue), it could have been removed more cleanly and with less damage. That’s why I described Marci specifically as having pasted the tab rather than gluing it. (My limited research had suggested that such pastes were used in medieval/Renaissance times—although that was based largely on Wikipedia, which isn’t always reliable. I realized though that glue was the more likely choice of the two adhesives, and so I mentioned it as well when suggesting further inspections of the original letter.) 
 
In Rich’s annotated image, though, there is clearly something that caused that thin band or streak running along the binding tab (which I had not seen -- good catch!) If it isn’t residue from paste or glue, then what else might explain it? What are the other bookbinding or expected codicological features seen in old books that could account for that elongated yellowish blemish? (I'm asking Lisa here.)