Well, the first thing I noticed is it isn't implemented for the FR client.
EDIT: Not implemented in the DE client either.
The EN client format looks like:
You are on server 65 at r2 lx1212 ly1538 ox85.67 oy49.68 oz711.87 h180.0. Game timestamp 413530581.868.
It turns out the server number is for the actual physical server within a cluster and does not have a 1:1 relationship to the World. For instance, three different characters simultaneously logged into Landroval had server numbers 64, 65, and 67 (they were in different regions) - heh just going through the door from ouside Erebor to inside Erebor moved me from server 64 to 52. Depending on their architecture, it may even be possible for one server to host regions from two different worlds (although probably only US or EU, not a combination due to database isssues). Since the physical servers that make up a cluster can be reallocated any time the servers are taken down for maintenance (and depending on their architecture possibly even while live), I suspect this value to be useless to Lua developers. I can see why SSG would want this for debugging purposes in case one physical server out of a cluster is causing trouble it will be much easier to pinpoint the affected server.