R.r.b. Cover - "Rail Road Business"

I just got an interesting cover, it has the corner with a preprinted slogan regarding use for Rail Road Business
This is for New Orleans Great Northern RR

I wonder if any of these every made it out "In The Wild" and were postmarked, delivered ?

Probably not. The RRB square is not a franking, just a warning to employees with access to the envelopes not to use them for personal correspondence. The sender would have affixed normal postage over the square. If they didn't, the cover would have been returned for postage.

Here is a RRB cover with letter sheet dated "March 27th / 1856" from Francis Painter, the wife of a newly appointed employee of the Cleveland & Toledo R.R. living in Elyria to her Husband, John Vickers Painter, probably being trained at the head office in Cleveland. Carried outside the government postal; service the 26 miles east to Cleveland receiving the railroads CDS (Towle SP-2) "Cleveland & Toledo R.R.".

This is an example of the illegal use of railroad business mail which could only travel on the companies lines without postage if related to railroad business.