On this one, imdb isn't correct. Watch the film. Then watch the closing credits. Look at the graphic in the background at the end.
A MERVYN LEROY PRODUCTION
Big letters.
That's credit.
Also appears at the end of the opening credits.
Oldmotem, that's a producer's credit. A director's credit would read "A Mervyn Leroy Film." There's a definite difference between the two.
shareno, it was typical in the 1930's & '40's (at least) to say "a [INSERT NAME] production" when addressing the director. i have seen this in hundreds of films of the period.
as you noted, it has obviously changed in the years since.