When Sam is trying to find out about Mary's friends, he asks about a Robert Campbell who died on the 19th of July 2001. July 19th is Jared Padalecki's birthday.
Sam states that changelings feed on synovial fluid from the mothers and that they always feed on the back of the neck. Synovial fluid is a type of fluid found only in the spaces between joints, it acts as a form of shock absorption it helps lubricate and also helps remove waste from the joint space. All humans have synovial fluid, not just women, and there is very little in the cervical vertebra. The majority of synovial fluid is found in larger joints such as the elbows and knees, so there might be other reasons as to why these creatures only feed on the mothers and only on the back of the neck.
Annette is reading "The Historian" by Elizabeth Kostova, a novel that riffs on the story of Dracula.
"The Cicero Pines Motel" location has been used many times throughout the shows seasons. Used in Hell House (2006) (S1 E17); Bloodlust (2006) (S2 E3); as well as LOTUS (2016) (S12 E8). It has had many different names in different episodes & a major remodel on the exterior for its appearance in season 12. The giveaway is the the "pyramid" shapes over the front doors or the wooden beams protruding from overhead. Those were covered though in the remodel.