The LOA is completely unrelated to Summer Seminar. You wouldn't get the LOA "at Summer Seminar". It is really a function of getting your application submitted, reviewed, and issuance of the LOA before Summer Seminar. It seems people have been referring to that as some sort of gold standard or holy grail, and I heard it has happened before, but I suspect that candidate truly walked on water ! Realistically, few LOA's are issued, Admissions is still focused on wrapping up this years class, and I have heard, anecdotally, that Admissions considered the early LOA's an anomally (or mistake). I wouldn't expect it to happen again but of course who knows what can happen.