See this post by Salsaguy on Jan 21, 2012:
https://www.mobileread.com/forums/sho...157184&page=26
He shows which keys had second functions and that was more than the top row. He did not mention that numbers showed on the keys in the top row.
Since the Kindle Keyboard Update, those other keys do NOT have second functions but the top row now displays the numbers. In addition, those second functions of the other alpha keys now are all on a distinct row separately displayed.