They note: “While T CrB clearly appears to be in the final stages before its next nova eruption, our analysis of its historical recurrence pattern suggests a significant scatter of at least 10 years around the mean ∼80-year period. Therefore, while an eruption is anticipated, the existing data do not allow for a precise prediction of its timing”.
Another NR which shows a scatter of about 10% of its mean period is M31N-2008-12a. The period is about one year with variability of about a month. The period so short that several eruptions have been observed.
The sample size is so small, IMO, that it is impossible to say whether this is typical behaviour.
Paul