That is from the Ford Shop Tips, Volume 1 Number 2 (November, 1963) that Ford would send out to the dealer technicians. I think it's safe to say that the 9 PSI was at idle only.
I have the owner's manual from the same time period that clearly states "occasional flickering" of the
oil light while idling is normal. Old Ford techs that worked at the dealers have told me that
"we would go as low as 6 psi at idle, but below that was usually bad."