Anyway, I was told b/c of the way the vent holes are it's likely a fake?
I see nothing wrong with vent holes.The brooch is made of two halves;the front is die stamped and soldered to the back, meaning the brooch is hollow.
Without vent holes it would explode when hard soldered under high temperature and acid pickling afterwards.
How can you expect to find many Art Nouveau examples of the same brooch ? Even two identical pieces is a success.
Btw.steel dies for stamping silver sheets are very expensive and profitable to fake only if hundreds or thousands examples are made on industrial scale.
In short, I think your brooch is genuine.
Regards