It seems to be an effect of the lume coating of the hands being thicker than that of the pips on the dial.
I found this to be particularly noticeable with my recently purchased vintage Caravelle.
The hands have a flatened tip where the lume is applied but the numerals are lightly painted over with a thin coating of lume. The numerals still light up, though dimly, but fade quickly. The hands stay lit around twenty times as long as the numerals.
View attachment 1078942
Notice that the numerals from two to twelve have a warm toasty hue while the number 1 is black because the remaining lume flaked away.
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