Let's pretend you are the president of a major automobile manufacturer with several brand divisions in your stable. The marketing folks and divisional managers insist that each brand be distinct in order to spur sales. But the dreaded guys wearing those green eye shades are equally insistent that it's too costly for each brand to be totally different from the others; sharing parts among brands will save lots of money and help profits.
By the 1930s the accepted solution was to generally side with the bean counters, but attempt to retain a degree of brand uniqueness. Before the 1960s when multiple sizes of cars became the prevailing mode, General Motors had five car brands and built them using two or three different bodies that were trimmed differently for each brand. In those days GM divisions designed and built their own engines, which helped to distinguish brands in a meaningful way.
I'll probably return to this subject again because I find it interesting. For now, let's take a peek at the brands using GM's 1949 "A" bodies that were intended for the least-expensive cars.
The 1949 A body was all-new, the first of its rank since before World War 2. A new post-war "C" body for GM's expensive cars was launched for the 1948 Oldsmobiles and Cadillacs and, months later, for senior-range 1949 Buicks. A-bodies were used by Chevrolet and Pontiac for all their production and for junior-range Oldmobiles.
As noted, all Chevrolets and Pontiacs used the A body. The brands had distinctive chrome trim that visually distinguished them, though from today's perspective the differences were surprisingly minor. Each make featured a rock guard on the lower leading edge of the rear fender, a functional necessity. Side chrome strips varied in placement and detail and the grilles differed. Pontiac also had its then-distinctive "Silver Streak" chrome stripes on the top centerlines of its hood and trunk. It also sported a short horizontal crease on the front fenders just aft of the headlights. The Pontiac shown is longer between the front door and wheelwell because it has an inline 8 cylinder motor and not a "straight six" as in the Chev.
These Oldsmobile series also used the A body. This artist's interpretation is slightly distorted, as was the norm in those days, but it serves to show the grille and trim used by Olds. Again, differences from Chevrolets and Pontiacs are not great.
1950 A-bodied Oldsmobiles were almost identical to the 49s, the main difference being a chrome strip on the front fenders. Compare the body to the Chevy in the top image and note the overall similarity.
This illustration depicts Oldsmobile's top-of-the-line 98 series that used the GM C body. The fender treatment is similar, but not identical, to that on the A body. And the upper part of the body differs even more. Oldsmobile stylists had the task of preserving brand identity across the two bodies, so grilles and other chrome trim details are similar. This assured buyers of 76s and 88s that they indeed were driving Oldsmobiles, a prestige step or two above Pontiacs and Chevrolets.
Today GM makes a greater effort to distinguish models from different brands such as the Cruze and Verano shown above. This effort includes different sheet metal on the fronts and sides, though the basic body structure is shared (note the doors and windows).