Saga of the Well World volumes 6 and 7 are recent additions which together comprise a new story with new characters.  The series should be read Saga of the Well World 1-5 then Watchers at the Well 1-3 and finally Saga 6-7.  From the foreword in Saga 7 (Ghost of the Well of Souls) the author intended to call book six "Currents of the Well of Souls" and the two volume project "The Sea Is Full of Stars".  It appears some misguided editor thought better, dropped the title, gave volume six the project name and royally confused the matter.  In order  to avoid adding to the confusion I've kept the publisher's confusing order taken from Saga 7 (Ghost of the Well of Souls) exactly as follows:


By Jack L. Chalker Published by Ballantine Books:
AND THE DEVIL WILL DRAG YOU UNDER
DANCE BAND ON THE TITANIC
DANCERS IN THE AFTERGLOW
A JUNGLE OF STARS
THE WEB OF THE CHOZEN
PRIAM'S LENS
THE MOREAU FACTOR

THE SAGA OF THE WELL WORLD
Volume 1: Midnight at the Well of Souls
Volume 2: Exiles at the Well of Souls 
Volume 3: Quest for the Well of Souls 
Volume 4: The Return of Nathan Brazil
Volume 5: Twilight at the Well of Souls:The Legacy of Nathan Brazil
Volume 6: The Sea Is Full of Stars 
Volume 7: Ghost of the Well of Souls

THE FOUR LORDS OF THE DIAMOND
Book One: Lilith: A Snake in the Grass 
Book Two: Cerberus: A Wolf in the Fold 
Book Three: Charon: A Dragon at the Gate 
Book Four: Medusa: A Tiger by the Tail

THE DANCING GODS
Book One: The River of Dancing Gods
Book Two: Demons of the Dancing Gods 
Book Three: Vengeance of the Dancing Gods 
Book Four: Songs of the Dancing Gods 
Book Five: Horrors of the Dancing Gods

THE RINGS OF THE MASTER
Book One: Lords of the Middle Dark 
Book Two: Pirates of the Thunder
Book Three: Warriors of the Storm 
Book Four: Masks of the Martyrs

THE WATCHERS AT THE WELL
Book One: Echoes of the Well of Souls
Book Two: Shadow of the Well of Souls 
Book Three: Gods of the Well of Souls

THE WONDERLAND GAMBIT
Book One: The Cybernetic Walrus 
Book Two: The March Hare Network 
Book Three: The Hot-Wired Dodo