I concur with the above. A paper that you are author on (no matter the position) that has been recently accepted for a publication is worth an update. Send it those schools that suggest they want updates. It wont be a huge impact under most circumstancesAny publication in a peer-reviewed journal would warrant an update letter, IMO. I would look at a school's specific admissions website to first see if they encourage update letters. Some will only accept them after an interview invite has been extended, while others will not accept them at all and specifically say not to send updates. If you try to send updates when they are unwanted, it will either be trashed or could be seen as not following instructions. It's still relatively early in the cycle, so if you think you will be accumulating more update fodder (presentations, volunteer hours, etc.) I would wait until you have a substantial amount to add to a letter.