I was a pinball addict from NJ in the 60's. When I had to go on vacation with my family to Lake George, NY & play add a balls, I felt like a junkie taking methadone. Add a balls might be more desirable to collectors because less were produced. As far as I know, they were all designed from the replay versions to reduce the total manufacturing cost & conform to the laws in certain jurisdictions that prohibited replays.

I'm sorry that I did not clearly answer the OP's question. Although, I wouldn't be surprised if there were add a ball games that were designed specifically as add a balls, I believe Palace Guard was a second thought to Royal Guard. I am very familiar with Royal Guard (one of Gottlieb's greatest) & can't remember if I ever even saw a Palace Guard. If I had access to a Palace Guard nearby, I would gladly look it over, but my gut feeling is that it subtracts from Royal Guard. I hope that you hear from somebody that can give you a real honest answer.