Thanks so much for your help! Could not get the door to budge by pushing. However, we could access the back of the door through the one adjacent to it. Could not remove all the screws on the back cover plate because the bottom two screws were blocked by the frame lip and weather stripping.
HOWEVER, DH noticed he could remove the bolts that held the frame-attached bracket to which the door latches. That let him free the latch and raise the door, after which he could remove the latch and discover, YES, the screw holding the lever was indeed loose.
One of the easiest fixes possible, and one we would not have known about without your help.
I love irv2.