I think I've misunderstood how this fits together, but perhaps I can be enlightened:

If I'm building a non-mixed sparsity, can I have multiple row and column maps?  I think yes.  If so, what does the sparsity pattern look like?  As a corollary, can I have multiple appearance of the same row and column maps.  Should the sparsity in this case be bigger than if I'd uniquified them?