That’s a good question Juan. But even with Events Calendar PRO you still only need to override the one file, that you already have.
Are you sure that the email you are referring to is the tickets email? Perhaps it is one of the WooCommerce emails. You could test for this by creating a unique override for each of those. Perhaps you could add the name of the file inside each override, and then do a test purchase to see which file is mentioned when you receive it.
Does that sound like a possibility?
– Brook