Predictably, john_tullamarine has sharpened the pencil. His question later in his reply regarding the age of the Pilot's Operating Manual Vs the AFM is very valid. If, at an early stage, the test pilot could only find, for example, 20 knots, then that is the limit and goes into the POH. At a later time if, say, 25 knots is found and is proven to be safe and controllable, the POH will be revised to reflect this.
On ya JT
Old Smokey