This line appears solid if enough ink got deposited in the space between the two printing plates. With your pair, it appears that there was not enough ink to completely fill in the gap which has resulted in it looking like two separate lines
Jogil... thanks... what's not totally clear to me is the thickness of
the line (if a single appearing as two with a lack of ink) versus the
comparison of the combo below, sold by Siegel, which shows a normal
and clean vertical line (noting as well, the 599A's are to the left)
Are there 2 actual distinct lines which are normally filled in with
a sufficient amount of ink, or was there some sort of "interlinking"
between the two Stickney plates which (regularly?) masked a 2nd line? https://siegelauctions.com/lot_grd....emailflag=on