Continuity mistake: In Ch. 72, Stu describes finding Harold dead, and recalls that "Harold still clutched the Permacover notebook in one stiffening hand." But earlier, in Ch. 64, Stephen King states that Harold "put the Permacover notebook into the Triumph's saddlebag" immediately before shooting himself.
Character mistake: In Chapter 62, Dayna Jurgens is talking to Randall Flagg. Flagg states that he has no intention of going to war, saying that "If humanity continues, let our grandfathers fight it out". He even repeats it; "Or their grandfathers". What Flagg must mean to say, is that their grandCHILDREN could fight it out.
Other mistake: In Chapter 59, Stu says that Nick "might have had his hands right on the shoebox", when the bomb inside went off. But Stu had no way of knowing that the bomb was hidden in a shoebox, he ran out of the house before it was even discovered. The only one who got close enough to see it was Nick, who was killed in the explosion.