Thank you, Bill, for your clarification...
Given the factor of only 40 lines per inch,
I guess it's reasonable and understandable
how the identification (could be achieved)
with the naked eye, versus magnification...
Quoting Siegel...
"Ribbed paper shows either horizontal or vertical ribbed lines at the rate of approximately 40 lines per inch"...
My only wonderment was why this most significant factor
was not exemplified with a scan by Siegel or recorded
elsewhere, given hypothetical cases of further discovery
of additional copies by a backscan...
Viewing Siegel's scan I can't see the ribbing...

Additionally, using the magnifier on Siegel's site
(link below) I'm still not seeing the ribbing...
http://www.siegelauctions.com/lot_g.../2020&symbol[]=All&lotclass=All&syear=All&pfoper=All&pseoper=All&pfgrade=&psegrade=&gandor=or&keyword=&catselect=eq&pscolumn=default&pssortby=&sortord=DESC&photo=&calledfrom=lkp