Could This Blank Back Possibly Have Printers Notations On It ?
 

We know the fronts were printed first so maybe this sheet was on top of a
stack instructing the printer to run off 100 sheets of whatever 350-460
back that press was set up for that day?

Nevermind.

The bottom number looks like part of a phone number.

Its funny how you said that,
i got a cell call the other day reading 000-000-0000. Of course i did not answer it, But i realized, i should of commended them for having such a unique number.
As to the OP- looks like it reads 350-460 like on some t206 cards, not sure what the 100 means

Grimshaw and a Rossman also had pencil, similar? There is a second Lake with no writing but similar brown markings.

http://i.imgur.com/vdhfVKx.jpghttp://i.imgur.com/k7s9Mry.jpg