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Why don't you have any doubts about those consecrations?  curious cause I've seen both of those questioned and "we claim that someone consecrated me two years after it happened, after the bishop's death" definitely seems sketch, and I know Thuc was kinda nutty.

+Thuc was certainly imprudent in many of his consecrations, but the bar for mental incapacity that would render him incapable of validly conferring the Sacraments is very high.  He basically would have to not have had any idea what he was doing so that he couldn't intend to do it.  People who know him testify that he was very sharp mentally (could switch between several languages in conversation with priest from different countries) even to the end ... but just that he was very susceptible to being manipulated emotionally.

As for +Mendez, there's actually a bit more doubt because of his having recently suffered a stroke prior to the consecration.  But even then, if he was capable of performing the Ritual, which is rather complicated, then it's extremely unlikely that he did not have enough of an idea about what he was doing to validly confer the Sacrament.

Church has always presumed validity even in the case of extremely elderly prelates who had to be helped along in performing the Ritual.

Father Jenkins delivers amazing sermons ... except that they're often very long and contain several sermons in one ... so that two hours later, while I recall that it was great, I couldn't tell you what it had been about. That could be partly due to early-onset memory loss on my end though.

Pius XII once rebuked a priest who went on for more than 1/2 an hour.