<p>I'd submit a "package" of supplemental material around the end of Jan. or in early Feb. No reason to go earlier, as they'll initially be focussed on sorting out the RD applications.</p>
<p>If you didn't do all the essays last time, then you could submit another now, but no need to go beyond the number initially requested.</p>
<p>Nothing wrong with an additional letter of recommendation --- IF its someone who knows you well; otherwise, don't bother.</p>
<p>DO update any grades, scores, EC achievements, etc. - at that time or whenever thereafter you have something worth reporting -and write a cover letter reiterating your interest in attending.</p>