Factual error: In Chapter 5, Koontz explains how Grandma Rowena started smacking her lips while eating, at the age of 75. He then says this same event happened "halfway between her seventh and eighth decades". But at 75, she is actually halfway between her eighth and ninth decades (or, if you prefer, halfway through her eighth decade) - much like the 1700s are the 18th century, not the 17th.

Factual error: In the library Lorrie refers to Pokemon cards, which weren't invented until 1996 (this part of the book takes place in 1994).