After 27 years, most of the concepts in "The Mythical Man Month" are
still accurate.Could you identify any one concepts that is no longer
accurate,and
discuss why it is important and why it has changed?

This may be a tougher task than it would seem.  See the comments from
Ed Yourdon, a computer author, when Frederick Brooks called him in
1994 about re-issuing the book:
http://www.yourdon.com/books/coolbooks/notes/brooks.html

Indeed many of the recent reviews are astounded at how relevant the
book still is.

Brooks called for examining software development under the rigors of
an engineering task; that might be one helpful way to do it.  Another
would be to see if Total Quality Management or Six Sigma-type programs
have had any impact on software design tasks.

Best regards,

Omnivorous-GA