I recently got the new edition of Highland Bagpipe Makers (Jeannie Campbell MBE) and in the extensive Glen section is reproduced the 1929 J&R Glen catalogue in which this page appears:
"IMPORTANT NOTICE.
Referring to the pitch of Pipe Chanters.
The particular attention of Pipe Band Presidents is drawn to Army Council Instruction No. 544 of 19th December 1928 authorising the change in all army bands from High Pitch to Low Pitch. This instruction must, in time, effect the Pipe Band as well as the Military Band*, and where massed bands play frequently together the necessity of the change is more urgent.
The High Pitch chanter hitherto supplied cannot be played at Low Pitch any more than a Bb Clarionet can play A nat parts.
For a number of years we have produced a Low Pitch chanter, A=439, more particularly for the use of stage artistes who desire to play along with Low Pitch orchestras (and) combined playing of Military Bands with pipes."
(On the catalogue page listing Bagpipe Chanters)
"All Pipe Chanters are made to Standard Army Pitch, Old Philharmonic, A=452.
Low-pitch Chanters are made to order only, A=439."
I believe that the terminology used doesn’t mean what us modern pipers probably think it means.
Certainly old chanters, if we label them as being in the key of A, are around A=452, that is, halfway between Concert A and Concert Bb.
But it makes no sense to make chanters, if we label them as being in the key of A, to the pitch of A=439 in order to play with Military Bands.
Why? Because Military Bands were based around instruments in Bb and Eb. Flutes were made in Eb (old terminology, Db in new terminology) for these bands.
And the mention of “Low Pitch Orchestras” almost certainly doesn’t refer to Symphony Orchestras but what we would call “dance bands” which included saxophones and clarinets in Bb and Eb.
So my assumption is that these chanters pitched in A=439 were not in the key of A, but in the key of Bb, in other words chanters that we nowadays would call “466” chanters.
*For those not familiar with British terminology “Military Band” is what we would call a “marching band” in the US, brass instruments, percussion, and woodwinds such as clarinets. It doesn’t mean military Pipes & Drums bands.