There is an alternative way from Alasdair to get to MhicChoinnich by continuing after Alasdair up onto Thearlaich and down climbing into a gap where the Kings Chimney at Diff. rating and will get you directly onto MhicChoinnich. I guess from this area below the start of the chimney will also allow you to also connect with the Collies Ledge? The times that I have been there I have always gone by the Kings Chimney and the folks that you came across after going by the Ledge will have gone by this route?
The way by the Collies ledge looks like an interesting way to get you there and maybe I should experience this way some time
but don't know if I will get up there again now that I have nearly reached eighty years of age.