einvoice-preflight already ran the Dutch NLCIUS national rules (BR-NL) on UBL files. Many Dutch ERPs and Factur-X exports use the CII syntax instead, and those files got only the EU base.
The builder build-nl-rules.mjs now also compiles the official nlcius-cii-1.0.3.13.xslt from the same Maven Central artefact: 34 national checks next to the 39 for UBL. A CII file whose BT-24 names urn:fdc:nen.nl:nlcius:v1.0 gets them automatically.
Tested on made-up files only: a clean invoice passes with no skipped rule, and a copy with a missing buyer reference, no seller street, payment code 10 and a buyer country subdivision draws BR-NL-2, BR-NL-3, BR-NL-12 and the warning BR-NL-28-2, each with an English fix. One thing the rules taught us: the usual empty ApplicableHeaderTradeDelivery element draws the official empty-element warning, so send a delivery date. No real Dutch invoice or Digipoort verdict has been tried yet.