The lettering on the coin is incuse, not raised, so can't be a filled die. Probably a broken die; the weakest pieces on the die tend to break off and the lettering is not stamped as a result.

I agree with the argument that there are too many of them to be an error, and not something that would usually be sorted out in inspection. I would call it a variety (although I wouldn't be interested in collecting this kind of variety).

TCR should consider coding all these partially lettered coin center chips as a variety, not an error. Which means don't give them a .E catalog number.