42: Meh. If you hold by the minority opinion that it’s only Assur Al HaYayin (which is probably the best Limud Z’chus for the Minhag HaOlam; either that or saying that everyone falls under the Rama’s Heter nowadays because music isn’t as reserved for royalty/gentry as it used to be), then a concert shouldn’t be a problem.
R’ Schachter says that if you count Chol HaMoed Pesach as part of S’firah, then you have to treat it like S’firah.
And Pashtus is that RebYidd is correct, at least according to the Shevet HaLevi.