I don't think it's 99% at all. I think it's a lot lower than that and increasingly so the last year, as usual. But I don't recall what some of the studies have shown it to be.
Way back in project Blue Book, it was 5%-15% as I recall of the top of my head--were bonafide UFO sorts of phenomena. I think those percentages have crept up year by year with the majority of GENERAL PUBLIC sightings still misperceiving conventional things as UFO's.
However, when one gets into police, military officers, commercial and military pilot reports, the percentages of authentic UFO craft being involved becomes significantly higher than the stats from the general public. Again, I don't recall specific figures.
Whatever it is, it's my opinion. But let's be generous and say that 85% are misidentification's by the general public. That leaves 15% as real, unidentified objects. That of course doesn't mean that they're alien craft, but only that they're unidentified. I think the remaining 15% are unexplained natural phenomena or perhaps Satanic deceptions.