If other folks have ideas about what may have caused these symptoms....
You need to understand we hear these symptoms over and over, and it's almost always a bad USB cable or a misunderstanding about how to check if your PC really is detecting Teensy.
Many, many times on this forum we've heard someone say pretty much the same things you've said, convinced their Teensy was dead, and then after getting them to actually try things in different ways, suddenly it turned out to start working again.
So I hope you can understand some of this skepticism you're hearing from us. Your boards may indeed be damaged. Without any info, and apparently *you* don't even know what happened to these boards, nobody here can even begin to guess what may have gone wrong.
But your main question seems to be asking for our collective knowledge & experience, based on what we've seen from others, rather than asking directly for help by giving us info & context specific to your problem. Please let me tell you in the clearest way possible, the things we see over and over are charge-only cables, misunderstanding how to check for detection of Teensy (Serial vs HID), code & driver issues that prevent automatic upload (but programming still works with the inconvenience of pressing the button on Teensy), and destroyed hardware. I can tell you cases of partial damage to the hardware are rare. Hardware damage is usually all-or-nothing. When something destroys the hardware, it's usually completely dead, often with the chip getting very hot.
So if your boards are showing some signs of life, but not communicating with your PC, I hope you can understand our perspective & assumptions when you keep asking for our collective knowledge & experience, with scant details on what you're actually trying, with little clarity on what specific problem behavior you're observing.