I recommend a critical review of the score sample from Trio en chaconne If you compare it with the edition in WIMA youll notice the initial motive in WIMAs edition has the notes   g  d a g a  b  in the right hand upper part while the sample in the Wikipedia article has  g  c a g a  b  Unfortunately Ive not access to the original printing of Livre dOrgue But from a music analysis point of view it seems obvious that the leading motive spans the chord on the first degree of the key in use in practice gminor The c found in the Wikipedia sample seems most unlikely to me