Well, thanks go to the author for setting me straight and pointing out my error. I cannot believe how simple a mistake I made... and it was staring me in the face the whole time.
As Charles mentioned in a comment on the previous post, many of these breadboards requires you to short the top and bottom halves of the left and right columns... I had done only one of each... you can see in the video that I've now used color wire to represent the positive and negative voltage columns.
Thanks again, Charles! I just knew that it couldn't be three bad 4026 chips...
Now I can get on with the rest of the exercise. (And be sure to catch the switch bounce in the video.)