How long does it take once an IMS starts to go?

[pothole]

Low values have nothing to do with the bearings failing. It's that they built loads of them. Now they're getting old but they haven't reached classic status.

Imagine a scenario where the bearing problem didn't exist and you assumed values of early 986s were higher. Well, you'd have to push prices up for all newer Boxsters, too. Because if you push up the value of an early 986, it becomes worth the same as a late 986. So adjust that up, too. Then it overlaps with 987s. Etc etc.

If you look at used values, the late 987s with 9A1 and no IMS are also depreciating and there's a pretty consistent slide in values as go down through the older models. There's no massive, massive drop in value when you go from an early 987.2 to a late 987.1. Yes, there's a gap, but it's just a normal gap given the 987.2 is the newer model.

There's just no space in the value hierarchy for early 986s to be worth significantly more than they are.

People tend to forget these are mass market cars. They built loads of them, so supply is strong. And most people who own them are not enthusiasts who spend the time to learn about this stuff.

Moreover, once you get to proper classic status, these sorts of issues completely fade away. People don't value 60s Ferraris on the basis of reliability.