I'm no expert so if we just stick to the FN made high powers (which includes those sold by Browning) the serial numbering systems for the HP have changed over the years. If you drop by here...
http://www.proofhouse.com/browning/index.html
And here...
http://www.browning.com/customerservice/dategun/detail.asp?id=35
You can see some of that change. In 1976 FN instituted the system that is still in place today with some slight changes. So for the HP we can see that the first 3 numbers will be:
215, 9mm military use. 245, 9mm sporting market. 2W5, 40 S&W caliber. There are others as well.
Browning now uses 510 for the 9mm HP but uses the same year code it seems. They don't say if they have changed the code for the .40 or not. I ain't sure about that.
The next 2 letters are the year code. In the case of this gun PZ indicates 1981.
The final string of numbers indicates that guns place in the number of guns produced that year. So if the number is 12345 it could be the 12,345 HP produced that year. Unless it is part of a special group of serial numbers set aside for a certain manufacturer which FN is known to do.
Now one book I have sets the introduction of the Mark II as 1982 and the Mk III as 89. Or close to those years anyways.
A picture of the gun we are talking about would be helpful. If you don't have one drop by here...
http://forums.1911forum.com/forumdisplay.php?f=15
There is a thread of pics of HPs and you can find one that looks like yours even if the finish is different and let us know.
tipoc