"Missing" districts in Staffordshire seem to be because they are using much more generalised areas as districts than on previous returns. E.g. if you put "Bilston" in the "Residential Place" Box, it does appear to limit the search further, but all the people returned are given as District=Wolverhampton.
Unless they improve on this, I think that a lot of money could be wasted trying to distinguish between people who would be differentiated by place on any other census.
[added: I guess that you can distinguish that the people returned as in Dudley, are in fact not in Dudley (examples I have found are actually in Coseley and Tipton) because if they really were in Dudley, they wouldn't be in Staffordshire]