The label would not fit
On this page11
The container was chosen first
Which fixes the panel area, which fixes the band, which fixes the minimum height. By the time the artwork is drawn, all three decisions have already been made.
The designer was asked to make the warning smaller
And could not. The table gives a floor in fractions of an inch and the only variable left is the container.
Point size was used instead of cap height
The regulation specifies "the actual height of the printed image of each upper case or capital letter as it appears on the label". A point size is a different measurement and the relationship varies by typeface.
The panel was measured as surface area
Including the shoulder, the taper and the part of the wrap that faces backwards. The principal display panel is what a buyer sees.
The design landed just over a band boundary
A panel at 5.2 square inches needs a larger signal word than one at 4.8. Designing close to a boundary without checking which side you are on is how that happens.
The signal word was set smaller than the statement of hazard
The table requires the opposite in every band above 5 square inches. The word that says how serious it is outranks the sentence explaining it.
The warning went on the back
Which the section on prominence, placement and conspicuousness exists to prevent. A front panel of branding and a rear panel of compliance is the arrangement being addressed.
The product was assumed not to be in scope
Classification depends on the formulation and its properties. Assuming a bike product is unregulated because it is a bike product is not a determination.
And nobody wrote the decision down
So the next print run re-derived it, differently. Panel area, band and heights recorded once per product is the whole fix.
The order that works
Classify, typeset at the required height, measure, then choose the container. Four steps, and only the last one costs money.