Hard to draw much from the data. Every year is different.
I know in Wisconsin, on a normal year the season is closed before certian species really move through in good numbers.
Bag limits also affect hunting pressure. When bluebills were reduced to 1/day, hunters targerted other species, some even passed on bluebills. Cans work much the same way. The data can't account for those variables.
Wet and dry years also have an impact on birds killed, fluctuating temperatures might send birds north and south and keep them in a certian state longer than normal, or might push them through a state overnight where they might have spent several days.
Lastly, we aren't as good at killing these things as we like to think. Harvest reports often paint a poor picture of what is actually out there, espeically in regards to things that migrate.