No...they don't do a study past 10 years! Most of these studies only covered a 10 year period (like 1990 to 2000). So, they take the survival rate (and it is the mean survival rate) of that 10 year period and express it in percentages.
There are very few studies that have been done over a 20, 25, or 30 year period, therefore, there are no numbers for that span of time.
So remember that the survival rate is based solely upon the period of years that the study was conducted.
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