This paper was primarily used to proof studio shots. When my eldest was born, a Montreal photographer provided us with P.O.P. proofs to see the various photos he took so we could make our selection.
Keeping the prints was of no consequence since the contrast was soft and the print would eventually fade as it was exposed to daylight especially if it was not thoroughly fixed, washed and toned. In any case a large stamp marked PROOF meant the photographs were unusable.
Thanks once again to George Dunbar for reminding me of the rich history we have in the TPL archive and the process of using studio proofs many years ago.