In theory, if you were to monitor when enough users are promoted to legendary status, it would be possible to reverse engineer what the secret seed is (you would however need to take into consideration that the required activity for each member may not be divisible by 14), although it would probably take more effort/work then it is really worth.
If you can find the secret seed by looking at when people are promoted, then you've (more-or-less) broken SHA-1's preimage resistance. This has never been done before, so if you do it, you should probably publish a paper about it.
