From "Paper Moon" to "Candleshoe": the mystery of the source material

In 1973 Peter Bogdanovich made a movie called "Paper Moon" after the successful book "Addie Pray" by Joe David Brown from 1971. It's about a con man and a young girl (who is perhaps his daughter) set in the rural midwest during the Great Depression. They make money by selling overprized personalized bibles to recently widowed women. Tatum O'Neal won the Academy Award for Best Supporting Actress for playing the role of the 9 years old Addie. The movie became a huge hit.

In adapting the book to film various changes had been made, but the stories of the book can still be recognized (I read the book). But only about two thirds of the book were used. There was still the last third of the book which describes the biggest adventure of the con man Moze and the little girl Addie: a rich old lady with a fortune should be tricked into thinking that the young girl was her long lost relative. A sequel of the successful movie was possible.

The studio wanted to make the sequel, calling it "Harvest Moon". But Bogdanovich couldn't relate to it. He felt the thing was done, he didn't want to go back to it again.
Instead of a movie sequel a TV series based on the movie was developed. The TV series "Paper Moon" was quite different than the movie and was no success. It was canceled after 13 episodes in 1974. In episode 3, "Imposter", they used material from the last third of the book: Moze prepares Addie to impersonate the long-lost granddaughter of a wealthy, tough recluse, but the plan goes haywire and Moze meets his match.
In the TV series the girl isn't played by Tatum O'Neal but by another child actress who looked very similar to her. Peter Bogdanovich himself had helped to cast her: Jodie Foster.

From that point on everything is only speculation, but I believe it's quite obvious: someone was still thinking about a sequel. The third part of the novel was too short for a movie but too good for a short TV episode. Someone tried to edit the story and made it into a script. Not exactly "Paper Moon II", that hadn't worked out well in the TV series. Something with a new name and new characters. Someone came up with that old book "Christmas at Candleshoe". They took only the title and a few elements from that book, basically the ending (the battle) and replaced Joe David Brown's US location with that old English estate: Candleshoe. The movie came out 1977.

I guess the movie rights for "Christmas at Candleshoe" were also pretty cheap, it's not a well-known book. Maybe this way they avoided to pay Joe David Brown again for the movie and title rights of his bestselling book.
And, of course, they would want Jodie Foster, the only thing from the TV series that was praised by the critics.