I find Guide lines interesting, so I started collecting them, here is Scott 300 top left margin sheet single with the lines crossing. One of my most liked stamp designs of the U.S Stamps.
Scott 300 pair One right hand guide line and one left hand guide line both would be middle of sheet, on this morning cover. 1906
Scott 499 Type 1, middle left sheet goods, 1923, could be also identified as a booklet pane 499E, guide line middle left. Note if purchasing a single on cover pay the lower price as a sheet goods type not a Booklet pane type. If there is no certificate from the experts.
Scott # 374A Booklet pane single, lower bottom guide line, Dec 24,1910, How i determined this being a Booklet pane was the upper right corner in much shorter and rounded compare to a sheet goods would be as long as the perfs on the side. A certificate would decide. If this is in fact a Booklet pane or a sheet good.It would then be considered the earliest used to date.
Scott 498E and 499E Booklet pane middle left guide line, Scarce usege of both same position booklet panes of different types on same cover, 1919 Feb 4