^^ that Sta Prest reminds me a lot of (something) Prest I wore late 70s in the light blue ice blue stapress colour. Exactly the same pockets, the keeper behind the fly rings a bell but no waist adjusters as I recall. Metal hook not button closure too and not that label but something white with '...Prest' on it. Also a straighter leg than the early 80s stapress.
I would welcome more discussion of Sta Prest/stapress - why does nobody ever seem to have had a vintage pair so we can have memories jogged with photos and talk details of pockets, labels, etc?
Would those have been ones that you got new off the rack in the late 70's or second hand/deadstock ones from earlier?