i've had 4 sightings there over the last few weeks, not neccessarily different birds, but yeh they're there alright! apparently seven could be a bit generous, the more conservative count is 5. from what i've heard from a couple of guys who spend most days there, there is only one which inhabits the delta area, whereas the counts of 7 include 2 or 3 in that area.
though i suppose anything is possible, i've seen them at brackenhurst near southwell, and across the river in clifton grove (only the 3rd recording there).
if you do go to attenborough, you will almost certainly see one from the tower hide, as thats where most are, and there are plenty of pairs of eyes to point them out (been getting hectic up there). IMO its a lot more rewarding to see them from the delta hide though, its so much more peaceful and natural down there (though if you're not familiar with the place, you have to spend £5 on a key for that hide.
got a bit carried away there

, good luck in spotting one though