Why is that disturbing?
Almost every single one of those chips had the ink of the cancellation removed 20 years ago and I am sure you know that. It is not something that has just happened.
You know that even though you cant see the ink, a slight tilt to the light, or just running your finger over it, will reveal the impression of the cancellation.

Very hard to take any view regarding chips that were 'altered' in any way long before we thought it was an issue, especially when their status is well known in the hobby, and they are properly described.

To date, I have not been shown one single 'alteration' that wasn't visible to the naked eye.
My concern, if any, is what undetectable alterations have taken place.

Would you (in your role regarding Standards & Archives) be making any suggestions/recommendations? I don't see how we can do anything other than treat any such occurrence on a case by case basis if required.