Do the decision letters for accepted groups ask them not to post that they were accepted? It seems like, after every funding cycle, no one admits they were accepted in these after-threads.
1) just getting picked to go to the interview really only gives you like a 1 in 3 or so chance of getting in to YC.
2) the news of getting accepted into YC is pretty
noteworthy and shouldn't be squandered -
it's useful for PR purposes when you launch your product.
If you blow the news too early, you miss out on a
potential PR-based influx of users from TechCrunch for
example.