Firstly,
@minutenrohr ended his post with IMO (in my opinion) thereby acknowledging what it is.
Secondly, the field of vintage watches is not one of absolutes but of opinions. If the opinions of others are discouraging, then you have likely taken them the wrong way. We are here to discuss watches and deepen our knowledge, not to deter people.
Thirdly, since opinions are nearly all we have, stating them should not be a crime. And stating that a steel Longines 13ZN from 1938, with a cursive font enamel dial, may not be original, is in no way outlandish. Even late 13.33 dials can be seen with the more modern serif font.
According to this 1936 advert, chronographs (a Valjoux 15 and two 13.33's?) could have cursive font enamel dials at that time.
But in this 1937 advert, the cursive font has disappeared.
Lastly, an advert from 1938.
Due to reduced water resistance as a result of having pusher(s), many 13ZN dials have deteriorated over time. It is not a surprise then, for an incorrect enamel dial to end up in a 13ZN watch as values increase. Furthermore, the odd subdial hands of your piece suggest that the watch has been altered in at least one way.
This is certainly a topic worthy of discussion.
P.S. All catalog images were taken from:
http://www.longinespassion.it/Longines_Passion/Benvenuto.html