The data does not support it.
Support what? Repeated trips on the same route(s) by the same aircraft?
or ash damage inside turbine hot sections being cumulative?
Thinking of the situation where fine-grained VA gets into the cooling channels inside turbine blades and / or forms a glassy coating on blades or stator vanes, therefore blocking leading-edge or other cooling holes, what's actually going to remove it? Therefore, further ash encounters must result in accumulation in the same area(s). If not, why not?