I am being inspired by George R.R. Martin and his A Song of Ice and Fire series which is currently at 21 years (A Game of Thrones was released in 1996) since the publication of the first work in the series and will only grow as the series is not finished.
What series in fiction has the longest time frame between the release of the first work in the series and completion of the series?
Answers should be limited based on the following:
- Fictional work of literature (i.e. not a film or television series, or novelizations based on the same)
- Installments written by the same author as the first work
- Be a completed series
- Can be different story lines but must be in the same "universe"
- Must be the same medium as original publication (e.g. Harry Potter was published as novel series, but Fantastic Beasts is a film series)