Since gum was applied by hand in those days, and there is a small area at the top that has no gum (which is common for gum not to go all the way to the edge), I always thought this was the top portion of the sheet....and this stamp on the upper row. The line is perfectly straight and appears to be the straight edge of the paper. There is nothing to indicate it was from a booklet pane and I don't know if they made booklet panes in 1893....That is really know.. Thank you for asking.