I amused myself looking at these 258 examples and seeing whether they were valid TEI.
It is rather sad to say that only about 30% seem to pass this simple test. Some reasons include
* TEI P4 not P5
* incomplete fragment
* no namespace
* reference to non-existent DTD
as well as the straightforward “wrong against the TEI” ones.
What conclusions one can draw is another matter :-}