I would have thought if the Menos are loads of souls merged in to one, then it would be more like the fusion process in DBZ. When the fusion ends, even though the personality of the fused being is gone the people involved in the fusion still retain memories of the former character.

Edit: Two things about the OP...

1) Where are you guys able to see an upgraded version of Chad's arm upgrade? It looks the same to me.

2) Who is the dude next to Ichigo meant to be at 1:04 mins in to the OP?
Ah that may be true, but then again I don't think Soul society can keep track of who was part of the menos, since there's barely any organization in SS's slums. Also the fact that i doubt Aizen would let anyone but his closest confidants in on his plans (i.e Gin and Tousen).

1.) Chad's arm looks darker and the red is a different color, other than that, looks the same to me.
2.) As for that dude, it was a faded image of ichigo in the BG that keeps flashing in and out, like with Orohime and Aizen before in the op