Hmmm I think that there are plenty of models who don't fit into the 5'9"-5'11" frame but I think those who are way out by two inches or so are only allowed in because they have exceptional bodies or faces. If you're outside the height guidelines but you have an amazing face, the agency isn't going to turn you down.
I don't think my face is particularly great (structure-wise

innocent: , but when I apply to agencies I tell the truth that I'm 6'0.5" and I've never been told that I'm too tall. I've had a few rejections that just say my look isn't right for them, and I've had interest from a few agencies too. But no one has ever mentioned that I'm over an inch over 5'11".
All the agencies lie... Michelle Buswell said herself on Fashion File that she's about 6'2" and she's listed by Marilyn's as being 6'.