In the moving scenes when the mirror is placed in the home office there is a Dell 2013 model flatscreen monitor on the desk. These events were supposed to take place in 2002. Flat screen monitors were a rarity and were much smaller in size.
In her chronology of owners of the glass, Kaylie mentions a Robert Clancy who acquired the glass in 1864. She mentions that while attending the University of Connecticut he was known as "the whale". The University of Connecticut opened as Storrs Agricultural College in 1881 and did not become the University of Connecticut until 1939.
When Kaylie is showing to the camera the pictures of past murders, when she's showing the first pictures her red nail polish is peeled off and then when she moves on to the next pictures her red nail polish is fresh.
When giving the story of the mirror, Kayleigh says its known history begins with Philip Lasser, 17th Earl of Leicester in 1754 who was killed by the mirror in 1755. In 1754, the title of Earl of Leicester was held by Thomas Coke. who was 1st Earl 1744-1759. There has been no Earl of Leicester with the surname Lasser. Two Earls were called Philip but both had the surname Sidney. There has never been a 17th Earl of Leicester; the farthest the title has passed was for the 7th Earls.