Quickest way to tell them apart is the thickness of the leaves. Iris swords are thicker like plastic. DL leaves are more like grass. Iris leaves also tend to stand straighter vs DL leaves that flop over. Follow down to the root base. Irises are on tubers and DLs have a root crown. I hope this helps somewhat. :)

Thank you honalee. My problem was that I tend to always choose irises with finer foliage - it was all sort of blending together after a while with the DL.
In the end, I must have put over 100 different day lilies at the bottom of my driveway for giveaway. Gone within 24 hours (yay) and my beds look so much more tidy without them.