It has always been rather simple. Having two regiments sharing the same name but being NA & EU was generally allowed because both community basically have zero thing in common besides the game they play on. Of course, if the regiment was EU lets say, and a new born NA regiment would come to take the name, it'd be appreciated that they talk to the leader of the 'older' regiment to let them know they would use the name but not in the same community/events and eventually could take a different tag aswell. McEwan for instance, some years ago, was quite good at explaining this to new regimental leaders.
When some retards tried to take the name of well established EU regiment in the late years (can't speak for NA since it's not my community), they got basically stopped right at the start, people telling them the name was already taken. If those newcommers tried to act stuborn, a moderator would come in and tell them how things are supposed to be done, closing the topic and eventually you would see the same regiment poping-up under a new name a few days later, or not.
The only thing is that, when regiment were disbanded, they couldn't hold on to the name which was basically free of use. Some people like the 14e for instance, were smart enough to keep the name and just turn as a gaming community, waiting for a game like HoldFast for them to use the name again.
That should be the community's role (which is for now composed for a huge majority of former or current NW players) to put a certain amount of pressure when some edgy kids try to 'steal' a name which has already been used a long time ago and/or for quite a long time. Eventually, moderators which have a deep knowledge of the community history could get involved if need is be but I believe that if you come on a new game, pick a name for your regiment, create a thread and once you've posted it, a dozen of people which are more experienced explain you politely and nicely that this name has already been taken by people using it for years, and that you're invited to change it as soon as possible, there should be in most cases no problem at all.