This article has some good information. It's certainly more than I want to know about warts.
> Isolated warts may remain unaltered for months or years, or a large number of new lesions may develop rapidly in a short period of time. The development of warts is not predictable. Approximately 65% of warts disappear spontaneously within two years. The patient’s age and number of lesions do not seem to affect the prognosis.
There are many different types of warts and of HPV. Since warts cause a type of dysplasia their life cycle can be very variable and unpredictable.