once Scherrie joined the group, mary is clearly working to position herself as the primary "leader" of the group, even if she does or does not handle all of the lead vocals. her mic is usually dominate [[although this could very well be distortions from years of bootlegs so hard to really judge this) and she handles the majority of the audience interaction and dialog. she also does about 50% or so of the leads

most of the MSC video i've seen still has a lead and 2 singers in terms of their position on stage. it's when Susaye joins that it becomes more of a free-for-all. they increase the amount of 3-part singing and also in the trading off of lines in songs. and they all seem to mostly use hand mics and work the stage.