For example, I believe KINGSMAN posted on the forums, saying that their tag was open to join, but when I went to the in-game clans page, it wasn't clear how to join them without a PW.

In my opinion, it is just an awkward user flow, which could confuse people trying to join a specific open tag. It would prob be nice to see a list of clans you can freely join with no PW instead of someone just knowing they can enter the tagId with no PW in the input box.

I wouldn't say it is game-breaking; however, it is confusing for a user.