Devs should make it like a real tournament with branching brackets. Then the problem would be solved.
The thing about this is, if you were to get prestige points for this situation, being the last clan to sign up and there happens to be an odd number of clans taking part in that week of wars, then you'll get every clan waiting until the last second to join. Each one hoping that this occurs and they get a walk until next week and a war wins worth of prestige.
Lol, the 11th clan could have joined in against Zaft Destiny. Zaft still would have done what they do
So what's the drawback in that? If you only got partial prestige (even every week) you wouldn't get in the final 8. it takes work to put a team together for a war n just saying they get to keep their current prestige as recompense is kinda weak. And signing up earlier doesn't necessarily guarantee you won't be last...