In the montage after the sanitarium murders, the first newspaper says that Mary murdered her family on August 4, 1892. The rest are August 4, 1985.
At the end of the beginning credits/montage a paper says "Seniors celebrate 20 years of Blood Night" & a picture below it says 'Blood Night '08'. Mary went on a rampage & killed everyone in the Psychiatric Center in 1989. So technically the paper is celebrating 19 years of Blood Night.