Volkswagen reportedly sold between 6700 and 17,000 pre-production vehicles to unsuspecting buyers in Europe and the US.
These vehicles were made for development, testing and other purposes and were not approved for general use, and in some cases should have been scrapped. Instead they were sold to consumers as new or used vehicles depending on their odometer readings.
Volkswagen has issued a recall for these vehicles.
A spokesperson for the brand said some of these vehicles could have been sold legally if the differences between them and type-approved production vehicles were properly documented. Indeed some vehicles may have only required a software update or a new navigation system to be road-worthy.
Other cars, on the other hand, deviated significantly from their production counterparts, and will need to be scrapped.
According to Der Spiegel, the figure of illegally sold pre-production models could be as high as 17,000, as a significant number of vehicles have an "unclear construction status".
The German newspaper also understands Herbert Diess, the Volkswagen Group's current boss and the Volkswagen brand's then CEO, was informed of the issue in 2016, but the company did not inform Germany's Motor Transport Authority until September 2018.