The scenes outside the school are filmed in present day. The school sign is showing an 11 digit telephone number with an area code starting with 012. The 01 prefix was not implemented until 1995.
When Lorraine Warren is dreaming about the demonic nun in her house, the demon actually reveals its name in 2 ways. The first is the way Lorraine realises at the end of the movie (written in the Bible). However, the audience is another way-the gold letters on the bookshelf behind her also spell out the name "Valak."