There are only two model years of P5 right now. 2002 and 2003, regardless of when you bought them, that's it. In Canada there is no 2003.5 to be released I don't think, but from the people at the Mazda dealership, it sounded to me like a 2004 model would be released, basically unchanged from the 2003.
The Mazda3 replacement isn't ready yet from what I understood, and the sales of the P5 are so good they might continue it another year. The dealership said they had expected to sell 5000 units Canada wide of the original 2002 release, and instead they ended up moving 2000-3000 per month.
In Vancouver these cars are getting to be everywhere, and while I find it interesting that the car could have such a short production run, making it slightly more unique, it also means that the aftermarket won't develop as well for it, which kind of sucks.