The European Chemicals Agency (ECHA) gave an explanation on new rules for REACH registration dossiers during a webinar in February 2023. The new rules follow changes made in 2022 to the annexes of the REACH Regulation that determine the information requirements for REACH registrations.
The changes are reflected in the latest version of IUCLID, which is the software that must be used for making REACH registration dossiers. That software already checks part of the requirements before submission of the dossier.
After submission of a REACH registration dossier, ECHA performs a technical completeness check in an automated process followed by a manual check. The rules for the automated process also have been updated, in order to deal with the latest changes in the REACH regulation.
More information: https://echa.europa.eu/-/completeness-check-of-reach-registration-dossiers-what-changes-in-2023-and-how-you-can-prepare