I get it, a timing belt slip is a stretch...

As far as subjectivity goes, with an n=1, its not subjective. There is clearly something that happened from my perspective. Others, like my wife and kids, also can make the clear distinction of its attributes before and after the event, what ever it was. And whatever it was, was not gradual but rather, instantaneous.

We collectively would not align on "smokey" is as we are uncalibrated, but we can all detect a clear and distinct meanshift individually. They (with a degree of disdainment) agree its significantly different.

I posted a video https://youtu.be/K_68pdbhyg8

This is my 4th Mercedes diesel (3 previous were 617's) spanning 20 years and over 500k miles of driving and wrenching merc diesels. A few weeks ago this 300D used to purr and put out a barely perceptible waft of smoke from the exhaust.

As you'll see in the video, its not that way now.