Questions on “Proprietary Proof” Obsoletes

KSorbo

I just pulled the trigger last night on this note and I’m having trouble finding any detailed information on “proprietary proofs” in general. I only found one other “proprietary proof” example of this note in auction records, so it doesn’t seem to be common. The lack of information has piqued my curiosity about the following:

1. When and why was the “proof” printed? Was it intended for collectors or for other purposes, such as an archive?
2. Who printed it? Was it ABNC? The note was originally printed by National Bank Note Company which I see was acquired by ABNC in the late 1860’s.
3. What does the “Property of ABNC” stamp on the back signify? Was it part of their archives? I’ve seen this on other proof notes as well.

Based on auction records I can see that this note has a lot of circulated examples, mostly in lower grades, and no remainders. The only other gem example I found was the other “proprietary proof”.

sellitstore

When and why was the “proof” printed? Was it intended for collectors or for other purposes, such as an archive?
1970s-80s and for internal use, to test plates, and determine availability for then current reprint projects, like souvenir cards.
Who printed it? Was it ABNC? The note was originally printed by National Bank Note Company which I see was acquired by ABNC in the late 1860’s.
Yes, ABNCo.
What does the “Property of ABNC” stamp on the back signify? Was it part of their archives? I’ve seen this on other proof notes as well.
Yes, it is from their archives, although there are fake "Property of the American Bank Note Company" stamps. The stamp appears on both genuine period proofs as well as these later "Proprietary Proofs". The difference between originals and 1970s-80s proofs is the paper. Original proofs are on India paper and proprietary proofs are on various other papers, usually whiter and thicker.
Based on auction records I can see that this note has a lot of circulated examples, mostly in lower grades, and no remainders. The only other gem example I found was the other “proprietary proof”.
Hundreds of different designs (maybe 1000+?) were produced as proprietary proofs during the 1970s-80s, but the total supply of all of these proofs is probably not more than several thousand. There don't appear to be any large hoards of the same sheet(s).
This is a beautiful note and much rarer in this form than issued. Prices are less than they might be for original proofs but, in many cases, they are just as rare. The vignette at center is titled "Turning Around".