I dealt with a recruiter when I was looking, and I did not plan on making the move unless I was absolutely certain that I passed the PE (and the only way was with the letter from NCEES).
I would suggest that (when you do start looking) to ensure that you put all of your chips on the table in regards to I have taken the test, but I have not received the letter, blah, blah, blah.
Most importantly, you could have some verbage placed within your offer letter. "I understand that you are hiring in at company XYZ as an X, but in the even that I receive the passing notification, my job classification will be changed to Y with a salary increase of Z or to a salary of Z".
If you have not found a recruiter, this may be the way to go, but I found that by utilizing my recruiter (would made about 30% commission of my starting salary) it was easier to negotiate.
I ended up interviewing with the firm that I am with now in mid-February, but I don't remember if I had my notification or not at that time.