Really? This is the first I've heard of that.

[He'd been about to question Dr. Lutece on how she could know that, but immediately the General adds that information and man, is that a lot to consider. Lutece had told him about alternate realities briefly once, but somehow he hadn't thought that would mean there could be more than one of himself.]

So... then this portal pulls not only from other worlds, but from mirrors of them, if I'm understanding it right.