In the discussion on the topic of the slots in the chin; I too am inclined to support the point made by Gerrit; the change occurred around mid '73 as a reason of introducing the US bumper style. But I will be hard to prove it, unless BMW factory documentation shows up, or a stack of NOS parts surface with different build years.
There is only one way to disprove the theory; find a pre mid-73 picture (not the car build date, but the photo date, think magazines! ) of a car with small slots. If one such photo would surface, then the theory is busted. If it doesn't surface.. well then it could be correct, or another explanation could exist.
( Looking at current state of Pre mid-73 cars will not tell you enough; the presence of short or equal length slots needs to be combined with unambigious data to prove that the nose has never been replaced. )
My May '73 3.0 CS has long, equal length splits. A replacement chin I purchased a few years ago was subsequently sold off after I realized it was the incorrect one...
Would It also mean that equal length slot parts are more scarce? About 23.000 e9's cars were sold prior to mid 73 with equal length slots, as opposed to 7500 cars sold post mid 73. (Wikipedia). However repair parts after mid 73 are more abundant vs the repair parts up to mid 73 (First in-first out stock principle? )