Reveal: All of the across grid entries contain the letters of the alphabet in order- 1AARIA contains the letter A, 5ABFG contains the letter B, and so on until you come to 42ASLEE which has no Z (nosy).
Thank you! Due to the caching I couldn’t see it when I solved… it is such a simple mechanism but so subtle! And quite a feat of construction IMO. Thanks again!