I think that they had suck a huge success with letters and numbers with rx7, that they decided to change over to all letters and numbers for their cars. Hence, mx3 mx5 mx6, etc. then they killed the rx so then they went to 323 626 mx5 (miata) and now they just shortened everything down so its simple. 3, 6, miata, rx8. Obviously for cars, not trucks: tribute, b2000, b2300, etc. My thoughts.
No, wait that made no sense. they had the 323 and the mx3 at the same time. Just ignore me, I need to sleep. Bad day at work lol. Night night...