The fourth gear was added for marketing reasons.
It was sandwitehed in between R and 2 for cost considerations.
The same basic design was used for many years and has proven to be be dependable if a bit akward.
My 2007 533 has the same 4 X 2 crashbox. It takes a bit of getting used to and fourth is a bit hard to find when shifting on the go but one does get used to it.