Thanks for the post. Tagging is quite a 'fun' subject :)
All the social platforms deal with tags in a slightly different way, and we also see differences in how content creators and game publishers use tags.
As you know, Twitter needs a unique tags or the social elements don't work. So we try to encourage this by a) preventing hashtags being used if they've already been used by another game, and b) blacklisting very generic words and genres to prevent false positives when picking up the content for the game publisher - when we launched someone tagged their game #game and it nearly sent our servers into orbit!
YouTube tagging for games is in the process of changing and YT recently introduced a curated game list, like Twitch and Mixer. On the one hand this will make picking up the content more accurate, but the downside is it doesn't work so well for content featuring multiple games or vlogs, so for now we encourage publishers to set a unique tag that works for the game and content creators - recommendations on YouTube rely on this, so when you see some channels tagging all their videos with GTAV, Minecraft, COD, and Skyrim thinking it will pull in extra views, in reality the opposite is happening.
Tagging isn't infallible, sadly, so while we try to be as accurate as possible when picking up content, we realise you guys still need the tools to fix tagging which goes wrong for any reason, or report bad tags like the Roguelike instance.
When you post or stream new content, we are using that tag to match the content to one of over 60,000 games in the database, then let the correct publisher or their agency know. We did experiment with using unique codes as tags, but it didn't work well in tests.
All that said, we're constantly trying to improve how content is being picked up and speaking directly to the platform teams, so we do appreciate your feedback. There are a number of changes coming around how content is picked up in the coming months that we hope will address these issues for you.