You can stare at something every day and not see it. Not because it is hidden, but because the frame you are looking through keeps it from resolving. The data was always there. NHANES has been running since 1976. Ten rounds, fifty years of blood-lead measurements, tens of thousands of people. The standard view presents each round separately, by survey year. Framed that way it looks like a series of snapshots, each more reassuring than the last, lead going down and the problem receding.
Replot the same data by birth year instead of survey year, put every cohort on the same axis, and a completely different picture shows up. It stops being a run of declining snapshots and turns into a generational signal, the shape of an entire population's chemical history, visible all at once. The technique isn't complicated. You just change what you use as the x-axis, and that choice decides what you can see.
I have some experience with the difference between looking at something directly and looking at it through a frame that makes it manageable. The frame is usually there for a reason. It does not always serve you.