Do cervical dystonia patients often have a long history of pre-existing neck problems, including significant stiffness that may last for days/weeks?

Generally Yes. 'Cervical dystonia typically begins in middle age, and rarely begins in adolescence and young adulthood. The cause of cervical dystonia is unknown, although a genetic susceptibility is thought to underlie some cases. If cervical dystonia begins in infancy or early childhood, secondary causes should be investigated.' Pl see attached info for some de.tails.
More than one type. There is more than one type of cervical dystonia as it turns out. You can read about it by doing a search for Dystonia. I've seen cervical dystonia present in many different ways.