The difference between a restruck
brockage and a die clash is that with the restruck
brockage detail/depth would be missing in the
incuse area since the die wouldn't make full contact with
incuse area of the
flan on the restrike, whereas with a die clash the detail in the
incuse area is (rather counter-intuitively) actually going to be slightly
enhanced relative to the rest of the coin... I drew this diagram for myself a while back to better understand what happens with a clashed die.
Ben