Don·t know if that is a record or not - I was told on first diagnosis that there was a 70% chance of recurrence- took that to mean there was a 30% chance of non-recurrence. Also that the longer you go without recurrence the less likely you are to ever have one. As you correctly said, every case is different.The most important thing with this type of cáncer is that it is usually very treatable if caught early. That means that you have to have to attend all of your checks, and probably for life, although if there are no recurrences the time between checks is extended. SO THAT if it returns, it is caught early. Presumably the patient on the fórum continued to have his checks throughout the 20 years.
I dont think reseeding is the problem, I think it is either a genetic factor, or a cell mutation due to exposure to a carcinogen ( smoking, alcohol, for example) - that is only my opinión.
Re worrying about it, that is something we all do, regardless of how long we have had a "clean" record, but as time goes on you will find you cope with it better, and can put your worries away in a box for longer periods, just letting them out when your check-ups are due, in the meantime just getting on with life.
Diane