For all you know, the LCD has already been replaced (and possibly the shutter too) and your camera will last longer than a "real" F3HP.
The F3HP does not exist as such. The F3 is the camera. Common nomenclature is to call the F3 with this prism an F3HP, but the camera is no different no matter which prism it is sold with.
Newer F3s were sold with the original prism. Some also bought the original prism to put on their F3s. Does that make these wrong somehow?
If you are buying to collect and historical accuracy is important, you need to do your own research. Most camera dealers sell gear for people use to take photographs. In this case, accuracy is not important; function is. Your camera apparently functions fine, and therefore it is what they sold it as being.
Finally, you can't rule out that the top plate was replaced at some point. That would change the serial number.
In short, unless you buy new you have no idea what you are getting. Any camera that has any significant usage on it may have a few or many unoriginal parts. As long as the condition is as described and the camera functions as implied by the description, all is good. My F3HP was sold to me as such and I have no idea how much of it came from the factory when the camera was new; the camera works, and therefore I am happy.
Jim MacKenzie - Regina, Saskatchewan, Canada
A bunch of Nikons; Feds, Zorkis and a Kiev; Pentax 67-II (inherited from my deceased father-in-law); Bronica SQ-A; and a nice Shen Hao 4x5 field camera with 3 decent lenses that needs to be taken outside more. Oh, and as of mid-2012, one of those bodies we don't talk about here.
Favourite film: do I need to pick only one?
FWIW - now back in NYC I checked my "Nikon Compendium". It states there that the F3HP is simply a F3 with a DE-3 viewfinder attached:
"The HP viewfinder, known as the DE-3, turns a normal F3 into an F3 HP, increasing the camera's weight from 700 to 745 grams. It is not just those with (eye)glasses who have come to appreciate the F3 HP, photographers with normal vision can benefit from the more comfortable viewing afforded by this finder so much so that in the latter years of its production the F3 was invariably delivered as the HP version."
(Heck of a run-on sentence there - BTW)
mate, you need some real issues in your life
your concerned whether your camera is 20 or 25 or 26 years old, because of something that might wear out after 10 years
worry about going outside and developing an eye for photography, knowing all this crap about dates and serial numbers won't make good images
My F3HP which was bought new in March 1985, has been used in extreme cold, -35ºC and extreme heat +45ºC.
For most of it's life it has travelled in a motorcycle tankbag and it does look very, very secondhand.
For what it's worth, the LCD display works pretty much as well as when new. I know this as I looked at a friends F3HP which recently had a new shutter and LCD screen fitted, both LCD units appeared identical.
I do know though, that in extreme heat, the LCD screen goes completely black. In extreme cold the LCD takes it's time in showing the display. Seems to have a lag, which is probably the battery working hard.
One of the advantages of the F3 body is the composition of the metal material. In extreme cold, your skin has less of a chance of sticking to it, compared to a steel body. I believe that this was one of the things taken into acount when it was being designed.
Be that as it may, I can tell you that in extreme cold, you need gloves so your skin doesn't either stick to anything or your fingers fall off.
In extreme heat you also need gloves. I use light summer motorcycle gloves, these gloves serve two purposes. Firstly, your hands sweat so much, you'll drop the camera in no time without gloves. Secondly, gloves stop your hands from getting sunburn.
If the camera works and the LCD is working well, I wouldn't worry, just run some film through it.