Unfortunately, it is not that clear.
Baunutzungsverordnung § 19:
The permissible floor area may be exceeded by the floor areas of the facilities specified in sentence 1 by up to 50 percent, but not more than up to a floor area ratio of 0.8; further exceeding to a minor extent may be permitted. The development plan may contain provisions deviating from sentence 2. Unless the development plan specifies otherwise, in individual cases the compliance with the limits resulting from sentence 2 may be disregarded.
It is not really clear whether the sentence in the development plan states that the limits must not be exceeded or whether, deviating from sentence 2, the floor areas may not be exceeded by 50%.
A reliable answer can only be expected from the building authority!