[Trail Goer]

Wow! I had to google that one, I didn't think it was possible, but you can tap trees in the fall after the leaves have dropped. You just need below freezing temperatures at night and above freezing during the day. It sounds like the syrup produced in the fall is generally not as sweet and most don't even bother collecting it. I'm not sure what the difference is and why the sap would be so different from Autumn vs late-winter and early-spring. I know and have known for a while that once the sap reaches the buds the sap changes and you don't want to keep collecting it after that.
Generally speaking (I know this varies depending on location and season): Grade A is late February, Grade B is early March, Grade C is late March and Grade D is early April. I've been told Grade D is generally reserved for recipes because the sugar content is so strong and not something you wouldn't typically serve with breakfast.