If we look at that chart, we can see that numbers from the 60s to the 80s are taken by 5 series, 6 series, X5, 1 series. Perhaps there would be an interference between codes, had the E46 been upgraded to, say, E56. Being that the new 5 series is E60, I'm guessing the older ones were in the 50s (not sure about that...if someone can look that up). Also, they had to account for other models, like the wagon and coupe (E91, E92). So I'm guessing the only free numbers were starting at 90.
