The various difficulty levels between test forms are adjusted by creating a unique scale for each form. Like I mentioned in another thread, missing 10 questions in one section of one form probably doesn't garner a score that is the same for someone missing 10 questions on another form. So if that June Math section was really that hard where everyone did relatively poorer, then the scale would be adjusted but you would still be compared to the 1998-2003 group once your scaled scores are derived by Harcourt.
As for your other question, I have read many times that Harcourt takes non-first time takers and creates a different scale for them. I guess my theory for why they would do this is that Harcourt wants to eliminate the possible inflation from your PCAT scores simply due to becoming "accustomed" to the exam. However, the Candidate Information Booklet makes no mention of such a policy. Most of the information I got was from this board and I don't remember any evidence that wasn't anecdotal. I believe someone called Harcourt about the issue but I'm not too sure.
I took the October 2006 PCAT and I'll be heading to Creighton in about a month from now. Though I would rather take the PCAT over the MCAT again, I don't really want to take either again.
I just try to create discussion here since this forum is slower than it should be. Coupled with my advisor role, I felt that I should know how the PCAT works inside and out in order to give accurate advice.