Is this slot on a European style lock cylinder normal?
Heracles calls your type of lock the &quot;carénée sésame&quot; (according to Google Translate, the &quot;sesame fairing&quot;, though a better English translation would probably be the &quot;sesame edge&quot; or &quot;sesame strip&quot;).
An example Euro cylinder from Heracles is the model SR series. In the pictures on that page, you will see that they are mostly standard Euro cylinders but there is one picture of a cylinder with a notch like yours. If you look at the datasheet, you will see that this model is labelled &quot;Spécial remplacement pour carénée sésame&quot; (&quot;Special replacement for sesame fairing&quot;). As far as I can tell, Heracles only makes some of their cylinders for this lock.
Because of the notch, they need to sell separate left-handed and right-handed versions of the cylinder, but I could not find anywhere they explain the purpose of the notch. The most likely reason would be to make sure you don't insert the cylinder backwards (since it is twice as long on one side, which doesn't seem to be very common), but according to the datasheet Heracles also makes other models of 30mm/60mm cylinder without the notch.

It also appears that the newer &quot;SESAME 2&quot; model of the lock no longer has this restriction, though it is hard to confirm that for sure.
Given all that information, the implication is that this was really just a method of controlling what locks you could use. That said, don't go grind off the notch on my say-so, because I don't speak French and can't confirm all this information for sure.