All seems to depend on who you ask and when.
Disney is very inconsistent about this for some reason.
If you have only a party ticket for the day you are going to the party then you'll want to book your other fastpass days first and then the party day.
And since many seem to get "flagged" and have their last day of fastpasses deleted if they contact Disney for any reason after making their fastpasses I'd suggest contacting for what you need prior to booking your fastpasses and then plan to not contact them after that.
If you have a regular ticket plus the party tyicket on the party day then you cannot double dip on fastpasses. You still only get the 3 and then after you use them can make a 4th etc.
Basically you cannot make 6 advanced fastpasses just because you have a regular ticket and party ticket on the party day.