Everywhere I’ve worked the NPD team had a pretty airtight process for pre-production units and the testing associated with each. To quote one of my engineering coljeguase it is “non-trivial” 
… Like Mike said, usually EV1, EV2, DV1, DV2, then a short pre production run of the line, then MP1, MP2, and so on. What has the client done in the past?