Help with timeline

I love this story. Read book 3 times, movie about 3 times, seen the play (a small local production about 30 yrs ago) and have also visited the site about 25 years ago. It was a record store, and the layout of the store, just like in movie (Frank's office just the same). It was a 20-plus yr. correspondence the first letter in the book was 1949. So they corresponded until 1969? That's when I read the book, about 1969. So Helene must have put the book out almost immediately after they stopped writing?

Comment: I hope the poster from 2007 who didn't understand this story has now matured enough to understand this beautiful story.