In order to meet the requirements for any lubricant, the lubricant specs HAVE to be known by both the additive company and the company blending the basestock. These requirements would include:
1) limits on sulphated ash, phosphorus, sulphur if applicable
2) High/low temp viscosity
3) Engine test requirements, including the duration of the tests, the rpm range and the engine load.
4) Oil performance standards, including limits on wear, deposits, oil consumption, change in viscosity,TBN retention and fuel efficiency.
VW DOES NOT have any secret tests with unknown requirements. If they did NO oil company could formulate a product to meet them, ie it would strictly be a hit or miss proposition. All VW can do is double check and repeat some of the testing that has already been performed and then add the oil to their approved list.
TS