I'm always amazed at America's inability to recognize great actors and actress from Britatin until at the very least they're in their fifties. More extreme examples are Ian McKellen, Judi Dench and Maggie Smith but we didn't do much better by Anthony Hopkins until he played Hannibal Lecter.
Mirren's a different story because while we didn't appreciate her movie work when it was in Britain until, let's be generous and says Gosford Park, we were more than willing to give her recognition for her work on television even if it was mostly British television. Well before we finally gave her an Oscar for playing Elizabeth II, she had been nominated for eight Emmys, five times for Prime Suspect alone. She is one of a handful of actresses to be nominated for two acting Emmys in the same calendar year. In 2003, she was nominated for THE rOMAN Spring of Mrs. sTONE and the TNT minor classic Door to Door. I'm also relative sure she holds a record for most Golden Globe nominations and wins in a single year: in 2007 she was nominated for The Queen (which she won for of course) and won for playing Elizabeth I in an HBO film. (This was not entirely icing, the limited series won Golden Globes for Best Mini-Series/TV Movie and Supporting Actor for Jeremy Irons.) And of course one of the actresses she was competing against WAS herself for Prime Suspect. (Also not entirely about her Clint Eastwood and Leonardo DiCaprio did the same in Best Directo and Actor in a Drama.)
Mirren seems incapable of slowing down in her seventies she's now acting in 1923 with a little known male lead named Harrison Ford. You could say she only gets better as an actress as she gets older but that would imply she was a slouch when she was in her twenties. She's just as great as she's ever been; it's just that we Yanks are slow to recognize it.