The explanation that was given to me is that schizotypal PD is the diagnosis given to people who show many of the signs of schizophrenia but do not experience florid psychosis. Schizoaffective is like bipolar with hallucinations and paranoia. I have no idea if that helps.

But the thing is, the diagnostic categories are both subjective and blurry. It's not uncommon to have multiple diagnoses, or to range between them depending on the symptoms at the time, or to have them changed when the mental health professional in charge changes. In my relatively short time in psychiatry, I was diagnosed with: depression, anxiety, OCD, PMDD, bipolar II and I, schizoaffective, schizotypal PD, schizoid PD, borderline personality, schizophrenia and psychosis NOS.
Basically, I learned that the diagnosis means **** all so long as you can find the coping strategies that work for you. Also good to know is that the drugs you might get from a psychiatrist are not especially correlative with the diagnosis; all the drugs are given for all the wide range of categories at some places.
Also if you can at all avoid it, getting the more serious diagnoses can have an impact on your ability to take out things like pritave medical, life, or travel insurance in the future; it can also affect your entry to certain careers. That's something I wish I had been aware of before I let them label me.