Just out of curiosity, can you tell you can't generate or check by yourself the matter of the availability of video content without using a proxy, maybe by engaging multiple non-network heavy parallel requests on the side of your server? I think I will check the issue and the available Twitch available API endpoints in more detail later.
Twitch names their server clusters with IATA, yes.
Twitch has many ingest servers where you send your stream and they all forward it to the main one which is in San Francisco, CA. So no matter where you stream from, it always goes to San Francisco.
Now, when a broadcaster starts his stream, he gets assigned a set of server clusters (for example: san francisco, frankfurt, prague, miami) and a set of server nodes (video12-video20, video36-video50, on each of those servers). When users connect to those servers, those servers pull the data from San Francisco and serve it. It always originates at San Francisco. It's their mother base.
But even if Amsterdam and London, or video2 and video71 aren't assigned to broadcaster, it doesn't mean users can't connect to them.
You can. Using my extension. If user connects to a server/node which is not assigned to the broadcaster, it still works like it is. The server pulls data from San Francisco and serves it to users on this node.
That's why it's potentially disruptive. When that happens, users are using server resources which are not assigned for this task, and may cause the "legitimate" users experience issues.
There is no way of knowing what servers and nodes are available to a broadcaster, unless you connect to Twitch API (Usher) from each location where Twitch has their servers:
Level3, edgecast, san francisco, seattle, san sose, chicago, washington, new york, los angeles, miami, stockholm, london, amsterdam, paris, frankfurt, warsaw, prague, sydney, hong kong, seoul, tokyo
Twitch automatically assigns you to the closest available node based on your IP geolocation, so unless you have TOR/Proxy/VPN, there's little you can do.
The way I described (with proxies around the world) is safe for Twitch because it uses their own network balancer.
If a broadcaster has only London and Amsterdam and you query the API from Korea and Washington, you will still get assigned to London and Amsterdam.