Hello,
This is a good question.
For half filled subshells, this is especially relevant for the d block metals. Elements in the 5th column of the d block (Mn, Tc, Re) have half filled subshells.
However, for the 4th column of the d block, with Cr, Mo and W, the stability of the half filled subshell is so great that one electron actually gets taken out of the s orbital and promoted to fill a 5d shell. This is the main significant exception for the MCAT.
Otherwise, half filled shells occur where one would expect, at d5, p3 etc.