I seem to remember we "oversaw" a number of referenda in Afghanistan and Iraq during our years of occupation. I don't think that makes it right, but it probably doesn't give us a leg to stand on.
If there were, I wager they not held with a weeks notice, without any involvement of local authorities while 80% of the population was on the run and the other 20% being terrorized in quite the way Ukrainians are in the occupied territories.
But of course referendums in the Ukraine are a joke given that big part of population fled the war.