> The Smithsonian Institution’s Global Volcanism Program has no record of any eruptions of Hayli Gubbi during the Holocene, the current geological epoch, which began at the end of the last ice age, about 11,700 years ago.

But I'm fairly confident that the Smithsonian's records don't go back more than 700 years.

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".

There will be some contribution to atmospheric makeup, of course. Whether that increases or decreases current insulation factor depends on what the cloud makeup is, where it rises to, how far it spreads, and how long it stays aloft.