I think they do get a letdown - they just don't feel it. I would think if you can't feel it, you would be able to tell by the baby's sucking action - nice long drawn out sucks.

People get AF back so soon?
Think I added that to my list before I realised the question was in relation to 'after a few weeks' of feeding. hehe. But I got mine back at 3 months I think some people do get it earlier.