[API Question] Cases in which ServerAdd and ServerRemove events are getting thrown

First of all: I don't know if this is the right sub forum for this thread or not; I find that the "support" forum is only for people with problems running lilypad on their server (in our case it is working flawlessly ).

My question is very simple:
In which cases are the ServerAdd and ServerRemove events getting thrown?

Some more background:
Me and my team are currently working on revamping our server (actually, a huge network) from bungee to lilypad and I am in charge of the lobby stuff. This case I wanted to approach the sign updates a bit differently and didn't want to update the signs in an interval. The current system works like it should, and we have no problems at all - except for detecting server adds and removals.

How can the lobby detect if a server gets added or removed from the cloud? The only way for me is to have a "sync" message to all servers and detect if something's coming back.

Any ideas?

i dont know anything about the Events, but you could, instead of the sync messages only send a "One-Way-Message":

So everytime a server stops a plugin sends a message to all servers, that it disconnects. (in the OnDisable)
And everytime it starts the Plugin sends a message to all servers that it has connected. (in the OnEnable)
But you would need to have this Plugin/Code on every server..

This would be a temp fix, but better than sending your sync messages.