Board Thread:Theories and Speculation/@comment-31338621-20190722212553/@comment-4849011-20190722221231

You could be right. It's also possible other Uchiha got it, but there was no record of it (sort of like how the Rinnegan was considered just a legend by some because until Madara and Pain, no one in modern times had it). I can imagine a Uchiha getting it during battle to avenge a comrade, then dying from wounds, leaving no one alive to testify about it.