It is a bit confusing because some hi powers have Ogden Utah stamped on the slide and some have St Louis and Montreal.
All Hi Powers are made in Belgium, with the exception of the licensed and unlicensed clones.
There are Argentine and Canadian licensed versions. There are Arcus and FEG clones.
There are probably more examples as I am not that well versed in HP's.
The frame was changed from a piece of milled billet steel to cast steel with the switch to the MK III which began production in around 89.
The MkIII is a considerably harder frame, but the durability of the older HP's is excellent too. The change was made to reduce production cost
The MkIII feeds hollow point rounds better and the feed ramp was changed to accomodate this. Many of the older HPs don't feed hollow points well or will only reliably feed certain types, mostly with the round nose profile.
All unmodified Belgian HP's tend to be very reliable. If you want a carry and shooter I would recommend the MKIII for the feed ramp change and the fact that in addition to the mag safety they also have a firing pin block.