How to average CDFs of one variable across years
Why don't you just take a weighted average?
Suppose you have ten years $t \in \{1,...,10\}$ and year $t$ has $N_t$ observations such that in total you have $\sum_t N_t=N$ observations. Let the year-$t$ CDF be $F_t$ with support $[\underline w_t,\overline w_t]$.
You can then define a weighted average CDF as
$$\overline F (w) = \sum_t \frac{N_t}{N} F_t(w).$$
This gives you a cdf, an increasing right-continuous function ranging over [0,1] with support $\cup_t [\underline w_t,\overline w_t]$. However, you have to pay attention to the individual supports, i.e., $F_t(w) =1 \forall w&gt;\overline w_t$ and $F_t(w) =0 \forall w&lt;\underline w_t$.