Alia Vox booklet (in the rip, Artwork/Booklet.pdf, p. with the track list): "Enregistrement realise LIVE a l Opera Comique en mai 2017"; the same page notes the performances ran 26 April - 7 May 2017, so the label distinguishes the run from the month the recording was taken. Year 2017 already correct; the folder name 2020 is the Alia Vox release year (c Alia Vox 2020).

Migration: a zero year, month, day or OperaClass id meant the value was unknown, not that it was zero. Set to null.