I believe they will use CRAs to try and validate the information; if the CRAs say it’s all good then they let you through, otherwise they hold it for manual review and might ask for more information.
I’ve actually brought this up before, the idea of “training” CRAs by opening utility accounts (who don’t really check nor care about your identity) under a fake identity, in order to then use that to pass KYC at Monzo or an equivalent bank: Credit Referencing Agencies - are they a necessary evil?