The oldest IE I know of would be Alachia. She's the only one who is hinted at knowing the ancient magic of naming. If might predate Wyrmwood, but not Oak Heart. Elven history and myth all start at that source, with the sole exception of the seven heroes who enter the city of the passions.
Ah, sorry about that then.

Of course they werent and couldnt be. Caynreth was and so were probably a few other children, but for all the events to take place there had to be elves in wyrmwood allready both as mates for Alamaise and parents to the "dragonkin" children.
What I was refering to was that the elves that inhabited Wyrmwood at that point (When Alamaise wanted new servants and made his deal) weren't actually from Wyrmwood. The true *place* of origin for elves is unknown, though my bet for the first elven civilisation would be Sereatha, the City of Spires.
A fictional timeline would look like this:
01. Races are created by Nightbane
02. Dragons take their domains among them Alamaise claiming what would become Wyrmwood
03. Namegivers became Namegives by entering the City of the Passions.
04. Namegivers spread over the world, founding civilisations. Sereatha is founded among others.
05. Elves enter Alaimses' domain. He lets them because he lusts for servants.
06. Alamaise is lonely, the passions create Oak Heart.
07. Alamaise deems elves unfit to serve him and makes his deal with the passions. He mates with severall elven women.
08. Caynreth is born, possibly others and raised by the elves that live there.
09. Centuries or Millenia pass, and the elves forget the buisness with Alamaise. Caynreth as the first elf created by the passion becomes their legend.
Dragons in general consider Alamaises' attempt to create servants a failure and turn to their creation of drakes.
10. The elven court is formed, basically it is justified on the (wrong) legend of Caynreth and the presence of Oak Heart in the Wyrmwood. Melyora becomes the first elven queen.
11. Shosara adopts Human boat designs, an outcry runs through the elven court. Dallia decides to travel to Shosara and is slain by Alamaise.
With all this, we have to keep in mind we are talking about growing civilisations with ties to each other. There is no telling how many children resulted from Alamaises mating and what they did or where they lived. We know for a fact that several of the Immortal elves originate from Sereatha (Harlequin, Ehran, Alachia and I believe Aithne.), so I would say it is a relativly safe bet that at least some of them went there and had children of their own. This would be reasonably placed at point 8 of the timeline above.
What became of Caynreth is unknown, but legend has it that she is one of the 9 heroes who created the heart of heroes. This however conflicts with the legend that the HoH was created by the 9 who enter the city of the passions.
My personal guess is that Alachia is one of the original children of Alamaise. Noone really knows where she came from or how she ascendet the rose throne. While she claims to have originated from Sereatha, noone knows for sure. She is far older than all of the other IEs and wields magic beyond any of them, with *maybe* the exception of Harlequin and Ehran, though neither of them knows the magic of naming. Alachia is one of the big enigmas in earthdawn and even when sourcebooks spoke of her they told little more but what the rest of the world *thought* to know about her. Her inner beeings are almost always left in the dark and she hasnt opened to anyone in all her years.
My second personal guess is that Harlequin knows and this is the reason why he could do whatever he wanted at the elven court without her so much as looking angry at him.
In Endless Worlds Aina hints at the wrong the elves have done the dragons, while Harlequin takes a rather typical stance. I personally believe Aina is one of the few who knows of the true history and took the dragons side as their creator. However, this is a guess.
There may have been other dragons creating IEs, but I have never read anything that would suggest this aside from the fact that some IEs originated from Sereatha. However, I find the explanation that the IEs just traveled around and had children who also traveled around more likely than other dragons willing to repeat Alamaises' "mistake". This is also underlines by the fact that Alamaise had to strike a bargain with the passions for this to be possible. The details of that bargain are unknown, but with the parties involved it would have been something large. My personal theorie is that the passions wanted to teach the dragons a lesson and that they deemed the creation of new life their own turf (if anyones at all. Since the passions are the fragments of the splintered beeing of Nightslayer, it is questionable if they consider creation anyones buisness but that of their former collective self.).
I read the Ancient files more then once, and I will say it again, they are a resource to be proud of.

Just as a sidenote though, unless Im missing an Alias, isnt Hessler missing on that list? The elf from the Black Madonna novel? Severall things in the book, the least of which beeing his knowledge about Leonardo, suggest that he is one of the crowd as well. Though, not necessarily one from ED.