Actually you shouldn't have stopped, I was finding it fascinating. I am an ardent Weill fan, studied many of his works as well as participating in Rise and Fall of the City of Mahagonny twice, once from the coaching staff and once actually sang the role of Money Bags Billy, in GERMAN no less, acccchhhhhh. I have done 3 Penny Twice as a performer, both times the Blitzstein version, so that the changed keys didn't register, they are my normal. I have listened to several other versions, including the Lenya German complete set. Although I have good relative pitch, because I haven't listened to Blitzstein in close proximity to other versions, it never registered (Pun intended) that there are key changes. Thanks for the post and please feel free to add more details, I'm interested.