Good call Mattia. A good example of neck angle changing is the Les Paul neck angle having been a steady 4° for a long time in the Kalamazoo shop but varying when the factory upped and moved, new tooling and people build training were done. They were still Les Pauls :-D It's entirely possible that PRS' don't have consistent neck angles over time, although this is unlikely given heavy CNC work.
If you want to do an exact copy then you need to copy every last detail of the carve, height of the fretboard from the body etc. of the specimen you like. A lot of these can be thrown out of the window if you just determine the angle yourself depending on how you adapt the design to your building methods and skills.
BTW - isn't happiness spelt with an I? Sorry to jump in on pedant Tuesday!