I noticed the part production end date of 1977 ........and I also remember the Grill on the 1981 528i that I recently purchased for 5 speed tranny , has the same chubby 4 slat grill. So does a non running 71 2800cs with safety inspection sticker dated 1983( most defiantly a replacement the) On a running 74 which I purchased from second owner, and On another 74 non running E9.
I am now more curious to look . But I think the 4 slats are plastic slats. Which is what BMW started with in 74 for all thier 2002 models. Also the Grill on the 74 started to be wider and thicker (chubby) for 2002 model. Overwhelming majority of BMW production was 2002 model in 74.One would question if BMW, the manufacturer, made plastic slats on one model (2002) would they continue to make metal slats on another model(E9) ? Why would they do that ? We may have our preferences now but thinking about it back then in 74 having skinny or chubby would not have made much of a difference. One can argue if designers moved to thicker rims around the kidney Grill on one model ( 2002) they would do the same with other models too, wouldn't they ? Unless if they already have in thier possessions tooling and or inventory of parts for the 5 slats. Or production quantity for E9 was so low that cost cutting measures didn't mount up to much with E9 . Wait, bmw was losing money with E9 from day one , and they stopped production for 74. And only produced few 75 models for Europe. So my guess is that
Bmw intended and used 5 slats at the beginning of 74 year model while they had started the 4 slats tooling more or less same time as 2002 conversion to plastic components. They used up what they had in thier inventory, and changed to 4 slats once they ran out. They might had kept the tooling and perhaps produced more parts for resale. I now wonder aside from E9 and E12 which other model used the same 4 slats Grill ?
It is intriguing to continue this for me at least....