It will depend on why it failed and how badly it failed. Some faults are fatal and prevent scanning altogether while others diminish scanability and mean that a barcode will scan more or less reliably depending on what is wrong with it and where it is scanned.
The verification test includes a check of the GTIN for authorisation, correct allocation and correct formatting. It is possible for a fully correct barcode symbol to contain a GTIN that has a fault. In this case the result of the test would be a fail. The barcode may scan perfectly but it would be conveying bad data that could compromise the users' records.
Version 1.0 – Updated 25th October 2014