It appears that we have a smart fellow here! This morning about 15 minutes after eating, I was just about to take Sage out. He'd been playing with toys and bouncing around the house when he suddenly ran over to the back door and made a few little anxious squeaky noises.
At that point Denali was outside and he could see her through the glass door. At first I thought he just wanted to play with her. Then he turned and ran to the other door, leading to the garage and yard, making the same noises and sniffing around a bit. He has been in and out both exits enough to know that they both lead to the backyard.
I called him (he knows his name and comes when called) and opened the back door. Out he went and got directly to business! He's got it! No I certainly don't expect him to be reliable yet, but he definitely has grasped the concept! Not bad for 11.5 weeks old!