Re: Used by date
"Not under either of my Chromebooks."
I think some models had the date printed in the bottom. Anyway:
"Every Chrome device receives regular updates from Google until it reaches its Auto Update Expiration (AUE) date, listed below, subject to support from component manufacturers. When a device reaches AUE, automatic software updates from Google will no longer be provided."
Ref: https://support.google.com/chrome/a/answer/6220366
"Since I started using them, I have watched and awful lot of Wintel lappies die the obsolescence death."
Perhaps.
I'm typing this on my Win8 era laptop, and the (free) Windows 10 is still getting the monthly updates. It won't be getting Windows 11 (due to Micros~1 planned obsolescence...) but unless the hardware dies, it will have had way over 10 years of service life. HP ended BIOS updates stopped 2 years ago, so there is that, but wouldn't call it obsolete just yet.