There is a Wheatstone concertina in the buy and sell with reed pan pictures. http://www.concertin...showtopic=20073
The post WWII Wheatstones seem to have 4 or 5 variations (that I have encountered) on their reed and reed pan set up.
clamped traditional brass shoes and dovetail slots
clamped aluminum shoes and dovetail slots
clamped Aluminum shoes for most reeds and brass for the highest notes
Crimped and screwed down rectangular aluminum shoes
Crimped and spring clipped rectangular aluminum shoes (as shown in this instrument's pictures)
My take is that Wheatstone was trying to stay competitive and cut production times. I'm guessing attaching the spring clips may have saved time as opposed to screwing down two screws by hand.
Geoff Crabb or Steve Dickinson might have more insight into this,