IO540
The PFA permit exception from full factory approval for construction is based on the premise that the builder is building on an amateur basis. Kits have to be 51% built by the amateur for his use and education (was 500 hours until recently).
Any aircraft, which can be proved to be built on a professional basis, becomes a garden ornament. The only exception is distributors building demonstration aircraft, which is allowed.
There have been cases of kit manufacturers flying in competed aircraft and falsifying the build records, but this has not happened, to the best of my knowledge, for some time.
Rod1