Question:
A 2-6 cadre is forced to retreat onto a 5-6 XX. The 5-6 is then attacked, the result is EX. Does the attacker take 5 or 7 points of losses?

Answer:
See rule 9F1, “Retreats”. Since the previously retreated cadre “contributes nothing to the defense” and “is ignored for exchange purposes”, the attacker would lose 5 strength points, the same as the defender lost, not counting strength points which are ignored.

Source:
TEM 76