Complex sentence: A portion of the unbuilt shelters were replaced with foxholes, and a few völgyzár lacked anti-tank trenches, in case of two völgyzár less than 50% of works had been done.
Split into simpler sentences: A portion of the unbuilt shelters were replaced with foxholes, and a few völgyzár lacked anti-tank trenches. In the case of two völgyzár, less than 50% of work had been done.