Sword of Unbelief features Elys and Jervon sometime after Dragon Scale Silver. It was originally published (in 1977) before Gryphon in Glory (1981) but it mentions the Hounds have finally been driven from High Hallack, which places it after their appearance there, when Kerovan asks the Were-riders to join the war (in the Year of the Gryphon).
Now, in Dragon Scale Silver, Jervon tells Elys when they first meet, "In the spring of this Year of the Gryphon they met with the Were-Riders of the wastes and those will fight hereafter with us." which is in direct conflict with their appearance in Gryphon in Glory where they're actually present when Kerovan invites the Were-riders to join the war.
Here is my theory on how to reconcile this paradox: how was it possible for them to be present in 2 different locations at the same time? This story may be the key. After saving Elyn from Ingaret's Curse at the end of Dragon Scale Silver, they begin their travels which ended them up in the Waste where Jervon is kidnapped by the bandits here. When they defeat the evil "god", as it's last curse, it may have flung them back in time from when they were (after the Hounds were defeated, in the Year of the Hornet according to Year of the Unicorn & The Toads of Grimmerdale) to the spring of the Year of the Gryphon when they meet Joisan who is following Kerovan, shortly before meeting the Were-riders in Gryphon in Glory.
There is precedence for such time travel. The same year Sword of Unbelief was published, Trey of Swords came out. In that story, Yonan travels back in time with Uruk of the Axe to re-fight a lost battle against the Dark. (Judging by the title of this short story, one wonders if Sword of Unbelief wasn't intended to be published in Trey of Swords considering the three "Treys" are titled: "Sword of Ice", "Sword of Lost Battles" and "Sword of Shadow", but got nixed at the last moment?) That means, for Elys & Jervon their adventures could have happened like this:
Dragon Scale Silver- Elys meets Jervon and he tells her the Were-riders have joined the war (spring of the Year of the Gryphon). Elys & Jervon save Elyn from Ingaret's Curse (autumn of the Year of the Gryphon).
Throughout the Years of the Fire Drake and Hornet, they travel and have adventures until:
Sword of Unbelief- In the autumn of the Year of the Hornet after the Hounds have been defeated, Jervon is kidnapped by bandits from the Waste and Elys, with his help, must battle an ancient, evil "god" to free him. When they return from the spirit dimension they worry they may have to fight the bandits to escape.
When they leave the evil temple, they discover that they have been flung back in time to the Year of the Gryphon in:
Gryphon in Glory- Elys & Jervon meet Joisan who has entered the Waste to follow Kerovan. When Joisan is kidnapped by the Thas, they meet Kerovan and the Were-rider Herrel. They travel with Kerovan until they must part ways.
After that, they travel the Waste until they discover, Jervon tells us in:
Gryphon's Eyrie- The Road of Exile, which they travel until they reach the cliff with the Gryphon Gate in it. Elys opens the Gate and they enter, only for Elys to get swept up by "That Which Runs the Ridges" leaving Jervon trapped in the Gate until he's retrieved from it by Kerovan & Joisan.
Their time-bending adventures continue in:
Songsmith- Elys is kidnapped and for nine years is held in suspended animation while pregnant with her son Trevon.
The Warding of the Witch World- It mentions that in a matter of weeks after his birth, Trevon rapidly aged the 9 years he'd been held in suspended animation.