Percentage of PDB entries not available in PDB format:

4/2021: 1.0%
3/2022: 1.5%
4/10/2024: 2.3%

Occurrences:
help.js "entries in the Protein Data Bank"

notes.htm#pdbformat
notes.htm#errors Error Handling Tests

versions.htm version 3.5 improved item 18 (can stay at 1% as it was then, August 2021).

Proteopedia
https://proteopedia.org/wiki/index.php/Atomic_coordinate_file#Models_Available_Only_in_mmCIF_Format