Are Mad Men Ceilings Too Modern?

As you know, finding mistakes in Mad Men is "one of white people’s favorite activities on earth", so here's my tentative contribution. Don't these drop ceilings look a bit too modern, especially with those air diffusers?  Drop ceilings were invented in 1958 and were originally glued or stapled. The T-bar suspension system you see here wasn't invented until the 1960s.

Would love to hear from somebody who knows more.

-- the image is from here