EU Regulations oblige suppliers that are placing products on the EU market to register those products in EPREL.
For already registered models, products compliance is not at stake if you are still an unverified supplier, as the electronic verification was not necessary at that moment. Anyhow, after the transitional period, registration for new product models will not be possible for unverified suppliers.
Disclaimer: Please note that the European Commission cannot provide a legally binding interpretation of the EU legislation, as this is the sole competence of the European Court of Justice. Any remarks from the European Commission services are without prejudice to the position the Commission might take should related cases arise in a procedure before the Court of Justice.