According to the best synthesis she can make of Elven records, legends, and this new myth, the timetable goes something like this: Abraxas left the service of someone or something or somewhere called Tlanxla to follow Loec to war against the Daemons during the Great Catastrophe, then left Loec for Isha, then left Isha for Rhya, then got bonked by Kurnous for abandoning Isha (immediately after this, Kurnous shacked up with Rhya) then got bonked by Sigmar for... being a dragon, presumably. No records Mathilde has found postdate that encounter, but all accounts of the fight say that Sigmar only wounded Abraxas. And if the Cult of Sigmar is saying that Abraxas survived instead of taking the opportunity to add another notch to His belt, then he probably survived.
Interesting. Tlanxla is, as we all know, a ruined Lizardmen temple-city and also an Old One God of war who rides the sky in a chariot or something. Deathfang said that Abraxas joined the Old Ones in the city of Iz, which we have long suspected to be Itza, and the sidestory more or less confirmed that the continent of Iz is Lustria, so Abraxas being in Tlanxla or serving Tlanxla scans.
Tlanxla also makes an appearance in an Asur myth about the coming of Chaos, where Tlanxla's Sword of Judgement is apparently a powerful weapon in the hands of a daemon called Ulgu, which is stolen by Hoeth during the Coming of Chaos to aid Him in the battle agianst the Dark Gods. This may or may not be a metaphor of Hoeth mastering Ulgu - which according to Marriseth is the first wind He mastered according to legend, and whose rune is called by the Grey Order The Sword of Judgement - but if it is it then one wonders what Tlanxla has to do with it. Loec is obviously also associated with Ulgu, so perhaps Abraxas leaving Tlanxla for Loec during the coming of Chaos is some sort of metaphor for Ulgu? Or perhaps it's a lot more literal, the city of Tlanxla fell during the Great Catastrophe (and possibly Tlanxla Themselves - if there was an Old One by that name - died, since the sidestory says that the Iz team is doomed) so Abraxas went away and found someone else to work with. Maybe he picked Loec because of the Ulgu connection, or maybe because Loec already had good rapport with a great dragon (Loec and Draugnir were famously buddies).
In the myths told by Heidi it was actually Ranald who stole a sword during the coming of Chaos, before handing it to Verena. In that story it's Morr's sword, just like in the human myth Lord Ulric and the Making of the World, but let's assume all those myths are refering to the same event. I think a possible synthesis suggests itself: Loec, who is also Ranald, learned of a weapon of Tlanxla from His servant Abraxas who served Tlanxla, or possibly was given it outright. That weapon was later given to Hoeth, who is also Verena, or possibly that Loec and Hoeth teamed up to get that weapon, and possibly that weapon is Ulgu or something. And then we can keep going by saying that Isha is Shallya and Abraxas leaving Loec for Isha is a hint about the relationship between Ranald and Shallya, and then the whole Rhya thing is...uh....I'll get back to you on that one.
Also, isn't Loec one of the Cadai? Was the original quote in which Abraxas's second master was said to be one of the Cytharai a mistake, or did the Eonir who told that myth have a different conception of the Cadai/Cytharai divide (is that a thing? is the division of Gods into the two sub-pantheons at all a matter of debate among the elves?) or is it one of those famous theological discrepancies which the Eonir will surely refuse to clarify if asked about?