By that standard, The Dark Wheel makes it clear that Oresrians are a separate species to Thargoids. The xeno scanner in-game positively identifies the ships we encounter as "Thargoid". Therefore canonically, Oresrians have not been encountered in the game at all.
This is the opposite of what we are explained in Premonition:
*******************************
"
Society chuckled. ‘Putting two and two together now, I see. Yes, we have
two distinct dynasties of the Thargoids. One known as the Oresrians, the
other as the Klaxians. Unfortunately, both are heading in the direction of
the core worlds. A conflict is already taking place, a civil war between their
kinds. The Oresrians appear to be losing, falling back. From their perspective,
they’re retreating, using our worlds as mere cover in their bid to escape their
foes.’
‘These … Oresrians are what we’ve been seeing? The reports …’
‘Yes,’ Exo said. ‘They intend to carve a path through our civilisation and
leave us cast down on either side. What was once called a “bullet-shield” in
military parlance, I believe. They only mean to escape. Humanity will merely
serve as a convenient way to delay their pursuers.’
"
******************************
These are of course the opinions and believes of individual characters in the book. Premonition was written well after the so called 'Retcon'.
No player has ever seen a Klaxian Thargiod. They aren't in the game.
As long as they aren't in the game, FD have all option open. They can add Klaxians or they can leave out, without any need for an explanation or retcon.