Thinking about Christmas at midyear is nothing new. In the late 19th century, some American catalog-based retailers included Christmas goods in their summer catalogs. Shipping times being what they were back then, the fall catalog was cutting it too close. Then, starting in the early 20th century, various reports popped up of Christmas In July celebrations, along with rumors that Australia really did observe Christmas in July. One of the newest mid-year observances is June 25: the exact halfway point to Christmas, known to many as Leon Day. Here are four things you need to know. Leon Day probably started…