I was discussing this with the chap who owns 3 a/c at our club and apart from being an airline captain is also a licenced aero engineer.
He told me that the demonstrated component has nothing to do with aerodynamics or pilot abilities. The testing that results in this figure is based on landing in a crosswind using a crab approach where the pilot DOES NOT align the a/c with the runway before landing - i.e. they land with the full crab still on.
The published figure is the figure at which the undercarriage will structurally fail with that full crab still on.
This is why it is easy to land an a/c with a 'demonstrated' of 17kts in a wind with a component of 25kts in a wings level condition. Yes there comes a point where dynamics come into play, however, technique covers much of it.
As FFF says - if it doesnt say limit in the POH/FM it isnt one.
However if you fly under the rules within a club FOB and that specifies X-wind LIMITS...then they are legal limits and must be complied with.
I know one FTO where the demonstrated is 17kts but the FOB restricts instructors to 25kts and all other licence holders to 17kts.