If I run mkdir -pv, it works -p, but I do not get verbose output; however, if I run only mkdir -v, then the detailed output will look as expected. You can also notice that the long form -vdoes not work at all.
From my testing::
mkdir -p a/b/ccreates a/, a/b/and a/b/c/does not give output to the terminal (as expected)
mkdir -v d: creates d/and outputs mkdir: created directory 'd'(as expected)
mkdir -pv e/f/g: creates e/, e/f/and e/f/g/does not give output to the terminal (why?)
mkdir --verbose h: gives an error illegal option -- -(why?)
Update . I published an error report with Apple on this issue and received the following response:

, "-v ", , mkdir -v , , OSX, , .