Annex VIII of Regulation No 811/2013 specifies that manufacturers cannot declare more favourable energy efficiency values than the ones resulting from the tests and/or calculations at their disposal that will be part of the technical documentation that is to be entered in EPREL before the first unit of a model is placed on the market. However if in a later moment a supplier finds out that for a model that is still being placed on the market, ulterior tests results in lower or less favourable performances than the values originally declared in EPREL, he does not need to declare new values as long as the difference between the declared and the ulteriorly measured values is within the margin of verifications that can be used by market surveillance authorities and the product is not likely to be considered not compliant on the basis of this difference.
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.