Hi Joe: This is an interesting topic!
Yes, it's true that Lanza had sung something like 130 concerts (as
well as singing two operatic roles twice) by the time of the televised
Palladium appearance in 1957. However, we have to remember that this
occasion was only the second time he'd sung in front of an audience
since 1954 (or the third, if you include his brief appearance in
Naples!), and before that he hadn't sung in public for three
additional years. It's therefore not surprising that he was nervous.
It's essential for any singer to be performing regularly if he/she
wants to conquer stagefright. Even then, many famous tenors (as
Armando points out in his book) have suffered dreadfully from nerves:
Caruso, for example, and Corelli, in particular.
I think that Lanza always suffered from a degree of stagefright --
even when he was performing regularly in the 1940s -- but it doesn't
seem to have been a particular problem for him in his earlier days.
Any singer who doesn't suffer from stagefright is not usually worth
hearing, in my experience, as the absence of nerves tends to go hand
in hand with a lack of excitement!
I've read reports that Lanza appeared nervous (or at least shy) at
quite a few of his concerts during his final tour in 1958. One
reliable witness who attended Mario's concert in Manchester told me
that there was a lot of "wringing of hands" between numbers, but that
(as with the Palladium concert) the moment he began singing, all of
his nervousness magically evaporated and he was completely in control.
We also have to remember that he was unwell throughout this tour.