See title.
Use case: I reported T344635 on August 21. As the proposed tag does not exist, I didn't add it. Now (okay, yesterday) ITSTHURSDAY, the error hits production and duplicate T344964 is reported.
Please don't ask me (and everyone else) to remember mentioning things in wherever the most recent train blocker thread is. (many people wouldn't even know about that at all, and I regularly forget) My hope is that with the proposed tag developers can more easily find train blockers themselves before deployment. Perhaps a bot could even do it by posting any recently opened bug reports with the proposed tag in the train blocker thread, but I'll leave that to the bot ops.