You should be fine, I have requested it at least 10 times and everytime I was given the bassinet seat in the bulkhead with the bassinet brought out and set-up for us. Key is that you must try and request the bulkhead seats as that is where they attach the bassinet to the wall in front of the seat. Those seats typically can not be reserved online but you can request it when you call Etihad's call center and they will be put a note in your reservation for it. The reason they do not 'guarantee' is that if there are more requests than available bassinets then someone is going to lose out, so the airport then allocates it on a first come first served basis with priority given to those families who requested it and second priority to those who never requested it previously but demand one when they check-in. I would advise you get to the airport early and be one of the first to check-in to ensure you get the bassinet.