I'm dealing with the same situation along a fence-line -- weeds, bermuda, tree saplings. I sprayed a grass killer on it last summer to kill the bermuda (which did a pretty good job) -- now, when the Iris bloom this Spring and I can identify them, I'll dig them out and replant or rehome -- then spend the summer killing every inch of bermuda with a shovel and Round-Up. Maybe I can replant the the area next Fall. Maybe not until next year. Once bermuda gets entrenched in an area, you just play hell gettting it gone.
Your Irises in that older bed likely don't bloom anymore because of the crowding -- of their own rhizomes, and bermuda grass. Dividing and replanting in a different area will make all the difference in the world. You'll get to see your blooms again!
