The OUP has published a timeline of opera history full of the most elementary howlers.
The premiere of Tristan, for instance, is dated to 1845. Mahler’s Klagende Lied is not a opera. Nothing happened in opera between 1878 and 1900. An ‘electronic libretto system’ is supposed to have ‘revolutionised’ opera in 1983.
Oxford University Press calls itself ‘a leading music publisher’. On this evidence it knows nothing about opera.
h/t: Mark Berry