Large magma bodies found beneath dormant volcanoes, surprising scientists

>The team found that all of the volcanoes, including dormant ones, have persistent and large magma bodies.

I always thought dormant merely means asleep - as in not currently active, but may wake up at any time. This is different from extinct volcanoes, which would actually be expected not to erupt. Crater lake in particular has well established hydrothermal activity, which strongly suggests there is still something going on below and it may erupt again in the future. Any geologists can explain what the surprising thing here is besides the apparent difficulty to distinguish dormant and extinct?

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