securing the Montefortino A-question

[Gaivs Antonivs Satvrninvs]

I noticed the new Montefortino A has a closing system using a tab on the outside of the cheekpiece similar to the last version of the Gallic A. This seems like an unsecure way to hold it on. I've searched the database here and only see that appear on the British Museum,London one. I can't see it on the others or any other means of keeping it on the head. If this is the correct/best way, how exactly is it done?
Thanks.