Whether or not a volcano has erupted during the https://en.wikipedia.org/wiki/Holocene https://en.wikipedia.org/wiki/Holocene Epoch, roughly the last 11.7k year

Whether or not a volcano has erupted during the https://en.wikipedia.org/wiki/Holocene https://en.wikipedia.org/wiki/Holocene Epoch, roughly the last 11.7k years, is a common "how active is it?" metric for volcanologists - https://en.wikipedia.org/wiki/Category:Holocene_volcanoes https://en.wikipedia.org/wiki/Category:Holocene_volcanoes From there - yeah, zero volcanoes had modern scientific monitoring before ~1980. Some have a few thousand years of written records...well, at least of major eruptions. Nobody ever kept "what did the volcano do today?" diaries. So generally - eruption records depend on field geologists doing a lot of grunt work around a volcano, trying to work out details of its geological history. And in a very poor, remote country like Ethiopia - which has also a history of border conflicts, civil wars, and other nastiness - geologists both bold and well-funded enough to do such field work may be rather scarce. Result - an eruption record may amount to "we have no real evidence that it's done anything big since maybe somewhere around X-ish thousand years ago".