Last I checked when BMW releases a new 3 series, it isn't called a 4 series or 5 series. It's usually 3xx whereas the xx may change, if at all. Cars are designated by the model year and model of make.
That is incorrect. They call it a '3' series or '5' series, and following numbers are to indicate the approximate engine size (so 325 is a 2.5 etc) The actual models are designated E so it would be a BMW 325 E46 etc etc.
Edit - ignore me! I misread what you wrote.
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