Can you list my book with Nielsen instead of Bowker?

As a US-based company, ISBNdirect doesn't have access to Nielsen's database. All ISBNs we assign are registered with Bowker, the US national ISBN agency. ISBNs are valid internationally, so a Bowker-issued ISBN works on Amazon UK, Apple Books, Kobo, and other major online retailers.

Nielsen registration mainly matters for traditional UK bookshops and library ordering systems. If that's important to you, you'd need to get an ISBN directly from Nielsen.