The Spectator custom (I don't say law) for many years has been that if a word is not in Chambers, the setter says so - and, often, points to where it might be found. The practice of informing us that a word is not in Chambers has been tacitly abandoned during the last year or so.
Personally, I love Chambers; but, that apart, there is much sense in having an accepted (and adhered to) ultimate referee, whether it be Chambers, Collins, OED or whatever.
My fury with The Spectator is it has been unilaterally ignoring its own custom.
The only reason I buy the appalling magazine is for the crossword. My subscription will soon be cancelled.