Yep, at present the tags view will only pull in the last month (approx) of discussions/posts. This is why, for example, the gameplan archives appear to be empty tags.
As soon as we roll out 'Elastic Search', which could be as early as the end of next week, the tags will return all content held within them. It's a trade off we made pre-launch to enable the overall search functionality. Elastic solves all of this, and does so very well 🙂