Why is NBR rating getting priority over PCA/MPA ratings

National Board of Review (NBR) is an American organization which used to be an "unofficial clearinghouse for new movies" in the early 20th century; producers then submitted their films to the board before making release prints. Thousands of films carried the "Passed by the National Board of Review" text in their main titles from 1916 into the 1950s. NBR now announces the best films of each year (according to its members) & holds the NBR awards annually.

But it is NOT an official body of film certification in the US.

So why is the NBR's "Passed" rating is shown in IMDb (for movies released between 1916 to 1950) when there's a rating from either the Production Code of America (PCA) or Motion Pictures Association (MPA) is available???

Here are some of the many examples:

The Great Dictator (1940); PCA and MPA rating available, but showing "Passed": https://www.imdb.com/title/tt0032553/

Lawrence of Arabia (1962); MPA rating available, but showing PCA rating "Approved": https://www.imdb.com/title/tt0056172/

Sunset Boulevard (1950); PCA rating available, but showing "Passed": https://www.imdb.com/title/tt0043014

I've tried many times to delete the NBR rating of such movies, but every time they got rejected, citing "badly formatted", "unable to verify" or "does not meet submission guidelines" as reasons.

It should be MPA>PCA>NBR