They had dialogue coaches but it wasn't a general accent. None of those actors listed pronounced their vowels in the same way across the board, which people drilled in the same accent would have done.

I think now it is called SE or Standard English, and the idea is to have a uniform sound within different timbre. My speaking voice has been described as incredibly distinct. That said, when I read quizzes, people with English as a Second Language like me as I put the start and end in words