Info? B&S Silvertone "School Flute" Whistle.

Has anyone ever come across one of these? I bought it off eBay from a U.S. source some months ago. It is most definitely a whistle as we now use the term, not a “flute” nor a recorder. Standard 6 tone holes and in D, two joints, cork lapped tenon on body, socket in head, allowing for some tuning range; conoid bore. It is made from cocus or a similar rosewood -quite decent workmanship.
On the head it is stamped

B&S
L
SILVERTONE
SCHOOL
FLUTE

and on the top of the body it is stamped
ENGLISH MADE

And, for comparison, alongside my Jon Swayne boxwood D whistle

I have no evidence whatever for this other than a gut feeling based on general knowledge about British school equipment, but I guess it must have been made pre 1950s and most likely post 1920, perhaps before the general take over in British primary schools of the Recorder, under the influence of Dolmetsch et al. I think it unlikely to be pre C20th. I have certainly never seen one before nor heard mention of any such. Ironic really, as I have long argued (occasionally) with school music teachers etc. that the Recorder is a really BAD instrument to give en mass to kids on account of how difficult it is to blow it properly, even with decent quality instruments and careful teaching, hence the ubiquitous (in my generation at any rate) out-of-tune recorder ensemble and loads of nasty squawking. The whistle is much more forgiving and easier to blow at elementary level, even if it is essentially diatonic rather than chromatic (the argument usually trotted out in favour of the recorder by classicalists, disregarding that most school kids never progress beyond diatonic music in upper Junior/lower Secondary School when the recorder gets inflicted on them!).

Anyway, I digressed… the real point is that this Silvertone thing must have been produced in fairly substantial numbers, so where are they? I have come across B&S “fifes”/band flutes, but not whistles. Can anyone tell me anything about these? Has anyone else got one? Can anyone give an account of using them in school?

The present example is in visually excellent condition apart from a little scuffing on the beak and some minor damage to the edge of the labium. The windway was rather constricted - old swelling of the wood? - leaving a rather weak and breathy tone and severe disinclination to overblow without extreme force/sharpening. I have cleaned out and slightly deepened the windway and tidied up the labium. This resulted in the whistle playing somewhat sharp of A=440, though I couldn’t be certain of its playing pitch before working on it - it was too “fluffy” - despite the probable “Low Pitch” designation indicated by the “L” stamp on the head. I have as a result taken the plunge and replaced the tenon with a metal extension to bring it down to A=440. (Sorry, no “before” pics, only “after”. It was just a simple turned-in-the-wood, cork-lapped tenon in the same proportions as the replacement, but obviously without the collar ring. The ring on the head is original.)

This seems to be fairly succesful, and hasn’t seriously upset the scale-length/intonation, which, while not bad by whistle standards, certainly wasn’t spot on anyway. The main problem both before and after doctoring is a tendency to play rather sharp in the upper middle of the upper octave (G, A, B,) chiefly due to having to push rather hard with the air supply to get it to “break” and stay up the octave. Further tweaking of the airway and labium have somewhat improved this problem, but not eradicated it. I now have a VERY loud, slightly breathy whistle. I’m not an experienced fipple voicer - flute embouchures are more my thing, but I’m also wondering if I dare do any more to it…

Any advice or information would be much appreciated.

Pics now added to original post. Any thoughts, anyone?
Cheers!
Jem.