(note: shares are in decimals, not percentage as shown in legends)
I find that market share is a significantly more informative number than absolute sales, as the total market changed sometime quite drastically. My database doesn’t yet go past 1996, but it seems Pontiac settled into a fairly stable niche before its final demise. There is one caveat:
The total market is passenger car sales, excluding light truck sales. Total light truck sales prior to 1977 are not readily available, as they were typically lumped together with medium and heavy duty truck sales, back when trucks were all trucks. Since light truck sales really started to take off in the mid ’70s, this chart tends to make Pontiac’s share look better than it is, of the total market. But since Pontiac didn’t have any light trucks, it’s still fairly useful.
What’s interesting is that Pontiac’s mean market share seems to want to be around 7%, with periods of deviation.