I don't understand what you mean by "detected cancer" and "symptomatic cancer". Eg if a cancer is already detected then by definition it is impossible to screen for it.
vs
(Symptomatic detected) Hey, what is this lump here? Why am I so tired? etc...
Yes, the latter is more likely to be comparable over time but it will still have issues with changes in how likely someone is to report it to their doctor, etc.