Bro there are photographs of the concentration of Bishop Kelly
http://stpiusvchapel.org/pdf-site/RomanCatholic/special%20rc.pdf
Well, the photos in that link don't actually show the consecration taking place, but I believe that there is a video out there also. Plus, there were multiple priest witnesses who credibly attest to the fact that it happened. Only doubt about the Mendez consecration of Bishop Kelly would be that Mendez had recently suffered a stroke and reportedly could not recognize some members of his extended family who had been close to him. But the level of his cognition had to be no more than that he knew what he was doing, i.e. consecrating, and if he could perform the actual Rite, there's no positive doubt but that he was aware of it. Was he all there mentally? Probably not. But he was undoubtedly there enough to validly consecrate Bishop Kelly. I would not hesitate to receive the Sacraments from a priest ordained by Bishop Kelly.