As I said, H and Kiki, I was as surprised as you were. However, the OED does always make an effort to find the earliest verifiable use of words, so - in the absence of evidence to the contrary - I take their word for such things.
You may well have seen a TV series a year or two back called 'Balderdash and Piffle', featuring Victoria Coren. She researched such things and did manage to persuade the scholars at the OED to accept some of her findings. So, their minds are far from closed to new proof, which had to be in writing and pretty uncontestable.
Over to you to seek out your forebears' diaries or whatever!