Hatz, you are being a little economical with the truth there.
The approach speeds, stall speeds etc for every permit aircraft are tested and recorded. I do enough test flying for the LAA to confirm that. They may not have a POH but the figures are known and it is down to a good pilot to fly those speeds. When I am doing an initial test flight the first thing I look for is the manufacturers claimed numbers and go off and test as against those. It is rare to find a kit these days that is much outside the manufacturers numbers. I flew a CZW Sportscruiser last week for it's test flight for initial permit issue and the numbers were within a kt or so of the manufacturers claimed figures.