Other mistake: At the beginning of the series, Hope Summers' character is called Bertha Edwards. Later in the series she is Clara Johnson; still later she is Clara Edwards.
Other mistake: When Ralph Mason walks into Walker's Drugstore and asks to purchase a tin of pipe tobacco, the tobacco tin that Ellie puts on the counter has black tape across the top covering its brand name, which is "Tuxedo."
Answer: Those "boxes" are valences that used to be very common, before air conditioning. They allow for windows to be open during rain storms. They permit air circulation, without letting the rain in.