I imagine Ruth sending a postcard to each of her nephews and nieces at the same time, so I wonder if it's that she sent two bunches - one on 8/10 and one on 8/15 - or if she sent them individually on different days.
Since the postcard was addressed c/o Alma Stokey, I've listed it as a related document for Alma. Four years later, in 1929, when Laura sent a postcard to Kay in Woods Hole, there was a box number. 1929 was the year that Alma went to India, so maybe sending things to Woods Hole care of her no longer made sense.