although I'm not entirely convinced that all of the notes are in tune.    More expensive recorders would certainly be better.

It may not be "a given" that more expensive ones would be more precisely "in tune."

One well known and highly respected flute maker (of fairly expensive flutes) has the complaint on his website, that "all the Xb flutes are flat on the K." (I don't recall which flute key, or which note, but the point should be clear.)

While it would seem obvious to me that "someone" should tune one of the @$#!% things and thereafter make them like the one that's in tune, there apparently is "some rule" that prohibits doing this. It's quite possibly something to do with a "tradition" of which I'm not fully informed(?).

With the fipple flutes, there is significant acoustic linking between the "tube pitch" and the "mouth pitch," so it is possible to slightly "bend" the pitch of an errant note by "chin wiggles" of appropriate kind. I find some p'whistle notes much more amenable to this treatment than others, but can't say whether a competent whistler might be able to learn to do it easily (and automatically on a known instrument) wherever needed.

I would expect a similar response for a recorder; but I haven't messed with one in several decades.

John