Barnabas attacks a television during a live performance of the Carpenters singing "Top of the World." The song was originally released in 1972, on the album "A Song For You," but it wasn't released as a single or performed before a television audience until 1973.
The architectural style, detailing and furnishing (e.g. a piano) of Collinswood - which Barnabas and Angelique recognize from c. 1776 - are wildly out of character for that period, and characteristic of the mid- to late-19th century, rather than the 18th.
The train Victoria rides during the opening credits is the Amtrak "Downeaster", which started service in the early 2000s. The cars and engines are from the 1990s, with the post-2000 Amtrak logo. When Amtrak was formed in 1971, the trains had rusty, hand-me-down streamlined passenger locomotives and cars that were near the end of their lives.
Towards the end, when Angelique and Barnabas are in her office, the door opens, and Barnabas is chained into a coffin. The lid is separate. Later, when Angelique opens and closes the coffin, the lid is on hinges.
When Angelique visits Barnabas at his home for the first time after his return, they move to the drawing room. Angelique reclines on the sofa, and the inside lining of her right boot is visible. In the next shot, the lining has been reinserted into the boot, but it appears and disappears continuously in various shots where the top of her boot is visible.
When Angelique goes to look at the site where the Vampire has killed the workmen, she is wearing long black pants. In the Collinwood driveway, she is wearing black tights and high heel shoes. When she enters the house, she is wearing long black boots.
When Victoria arrives at Collinswood, her first conversation with Willie indicates that she has applied for the governess job under the name Victoria Winters. An earlier scene shows that she didn't invent the name until earlier that same day, on the train en route to Maine.
On the Amtrak train, the poster where "Victoria Winters" takes her name is for skiing in Victoria, BC. Victoria is on Vancouver Island, and with its temperate climate and lack of mountains, is not a ski destination (unlike Whistler BC, for example, which is on the mainland, and benefits from the Rockies).
The goof items below may give away important plot points.
When the townspeople bury Barnabas in 1776, a man with very distinctive long, blonde hair with some dark patches is on Angie's left. Barnabas was buried for 196 years. The same man appears in a 1972 scene showing the restoration of Collinwood. He appears at the start of the scene, as a workman in gray overalls, walking from left to right behind the car Willie is polishing.
Maggie Evans escaped from a mental institution and created a new identity; Victoria Winters. She used that name to apply for the job at Collinwood. When she rehearses her introduction on the train, she's clearly trying to avoid introducing herself as Maggie.