I have observed that B flat flutes and A flutes that are not Boehm key systems are also being called Flute D'Amour. These are not always older. Irish and other folk music still use B flat and A flutes with old traditional key systems. The reason behind these non Boehm system flutes still being used is the combinations of other instruments you are playing with and their inherent pitch and key. Very much like the D flat flutes and piccolos, the key of the music in which you play will sound very different on these instruments. Example: piccolo part in Stars and Stripes Forever - G major vs. A flat.
Enjoy the exploration of flutes in different keys. Having played E flat, D, D flat, C, and G flutes each having a unique beauty and place in performance, although not all are practical.
Currently, I'm dabbling with a pre-Boehm keyed German D flat flute (pictured below). Transposing to concert pitch greatly alters the color. Playing concert pitch flat keys make beautiful transpositions with rich color.