At the end of the series, Roderick's headstone reads "1950-2023", but in the first flashback from 1953 Roderick and Madeline are older than 3.
Around the time 14:24, you can see security cameras on the ceiling from the present, not the 1980's.
In the deal-making scene, set on early new year's day 1980, Madeline Usher lists a series of mythical deal/offer scenarios, ending with a joking finale of "What would you do for a Klondike bar?" That Klondike campaign didn't begin until 1982.