Here is chronology of the evolution of the ET9,3 Mahle wheels...
Of course there may be variants I do not know of.
View attachment 39952
Picture 1 :
Up to September 73
Ref 2900363
Mahle prototype, as seen on BMW-owned cars M-AW544, M-YM313 and M-YM709
The basketvawe is larger than on later Mahles
The part of the rim with "BMW" "MAHLE" "7x14" is thiner
The flat (horizontal) part of the rim is deeper
Intermediary row of holes in the basketvawe is an alternance of 2x open / 2x closed
No KBA number
XXXXX-rare
Picture 2 :
Sept 73 to Sept 74
Type RA33
Ref 2200529
Basketvawe slightly smaller than prototype
The part of the rim with "BMW" "MAHLE" "7x14" "2200529" is thicker.
The flat (horizontal) part of the rim is narrower
Intermediary row of holes in the basketvawe is an alternance of 2x open / 2x closed
No KBA number
Always silver
I have never seen a "pre-KBA" Mahle with the BBS brand (which does not mean they never existed)
Picture 3 :
Sept 74 to end of 75
Same as picture 2, but now with a KBA number : KBA40069
(The KBA nomenclature was introduced in the fall of 1974.
From then on every accessory had to wear a KBA number,
which was attributed after being tested by the TüV).
Now also available as Mahle-BBS aftermarket wheel :
Type RA38
KBA 40070
Ref 2900447
Markings "MAHLE -BBS" "KBA40070" "2900447" "7x14"
Available with silver or gold basketwave
Picture 4 :
1976 and 1977
Same as model 1975, but holes in the intermediary row of the basketvawe are all closed (the basketwave looks more "full").
This allowed the wheels to have a higher max. load, a change probably needed for the LWB E3.
Available as RA33 BMW-Mahle in silver and aftermarket RA38 Mahle-BBS in silver or gold
From 1978 - Flat basketvawe BBS
In 1978 (maybe late 1977) the "convex" Mahles were replaced with a new generation of 7x14 wheels, the RA86, with a flat basketwave and ET11.
New KBA is 400160
They are marked "Mahle-BBS" and "BMW".