In a flashback scene, identified as taking place in 1956, Sophia mentions watching "Your Show of Shows" the previous evening. That program ended in 1954.
Sophia carefully takes a cake pan out of the oven using oven mitts and then carries it into the living room. When she places it on the end table she holds it with her bare hands while placing the mitts on the table under the cake pan.
While the girls are recalling birthdays past, they discuss the first time they threw a party for Blanche, which was shortly after they all moved together. However, in an earlier episode, they found out Blanche's birthday by pressuring Blanche into telling when her birthday is.
In the flashback scene when Sophia stops by before Blanche's surprise party, the make-up department has Sophia looking like she currently does, not the way she looked in the pilot episode when she was also living at Shady Pines. Her glasses and hairstyle were quite different then.