Meteoritical Bulletin entry for Uasara. I have only a few things to add to the above description; Sierra Gorda and Negrillos are both described as being heavily weathered in Vagn F. Buchwald’s Handbook of Iron Meteorites. The “ragged” surface noted in the description as evidence of weathering is a late fracture covered with frothy fusion crust (see images). So, this isn’t paired.
In fact, given the pristine condition of the meteorite, I see little reason to doubt the finder’s story; Uasara is likely a witnessed fall. This iron is featured on page 64 of the Field Guide to Meteors and Meteorites, by O. Richard Norton & Lawrence A. Chitwood. It is a remarkable example of an oriented meteorite.