Posted By:
MattI arrived at my understanding by watching the threads over several months and I don't recall seeing someone ever post more then once per pickup thread (aside from a comment on another's pickup). As far as it being impractical, I'm certain the majority of us don't post everything we pick up each month - no one would need 16 or 17 pickup threads 
As it seems everyone besides me read it as modifying the thread and not the person's pickup, I shall correct my understanding accordingly.