Beckett gets one wrong.
I came across a listing on Ebay that advertised an autograph page featuring the signatures of Barry and Robin Gibb with a Beckett LOA. The page also has the signature of Hollies lead singer Allan Clarke. The seller listed the item as "Bee Gees signed. Barry and Robin Gibb. Beckett Certificate". I immediately realized that Barry Gibb had not signed this page. The signers were actually Robin Gibb, Allan Clarke, and Vince Melouney...the original lead guitarist of the early Bee Gees. I think Beckett didn't have a clue so they merely went with what was written on the page by the person who obtained the signatures. The certificate is dated April, 2022, so it is quite recent. I have included a scan of an early set of Bee Gees signatures which shows the difference between Barry's and Vince's signatures. I don't know how Beckett can say they noted "mutliple factors common to known exemplars" when comparing the "Hi Vince" signature to anything signed by Barry.