After trying out several combinations with /r and /f and without /r, the one that worked for me perfectly is:

@echo off for /r %%f in (*.jpg) do ( "C:\Program Files\ImageMagick-7.1.1-Q16-HDRI\magick" mogrify -gravity South -chop 0x42 -shave 14x0 "%%f" )

This worked beautifully across the base directory and all sub-directories and nested one's too :) Thanks very much for the tips!