Take copies. That is the point.
These are the actual files, not a player. Right-click and save, or tap and hold. Put them somewhere that is not this website — a laptop, a drive, a phone, someone else’s computer. Copies spread across several houses survive things that no single hard drive does.
The letters are not listed here. Each one downloads from its own page, reached by the code printed beside it in the book.
The masters — the full-quality recordings, the session files, the scans at print resolution — are too big for a website and do not belong on one. They live on drives, with a copy kept in another house. Ask.