Back in the good old days, CZ never have been importet to the US by any company. They had been imported or better taken to the US by US Soldiers, that had been stationed here in germany and that bought the CZ`s at Frankonia, that is the main importer for CZ firearms in germany.
I can`t tell, when CZ started to sell directly in the US, but it can`t be that long ago, compared to how long CZ75`s are on the market.
Since specially the Pre "B"`s had been purchased in a germany shop, they mostly all have the german proof marks on them. Later models, that hadn`t been sold via germany, would most likely not have these proof marks on them.