Arthas' non canonical visions of the shadowlands? If recontextualizing existing lore is a retcon to you, then all of this is a retcon because none of this was intended at the time of Wrath. These devs weren't even working on Warcraft during Wrath. The Helm of Domination literally coming from the shadowlands was not canon until they announced the Shadowlands expansion. But I don't think giving more context things we've only gleaned should be considered a retcon.
(Also, Loken made the Tol'vir. Not a titan, in fact, Loken hated the titans. It's never said anywhere Kil'jaeden made the Lich King's armaments, just that he commissioned the dreadlords to acquire them. And at this point we don't even know if Arthas knew about the Shadowlands: We can only assume he might have because Bolvar knows about the Shadowlands. While it is implied that Kel'thuzad had extensive knowledge of the Shadowlands as he apparently came & went from them as he pleased.)
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"This ornate box is covered with webs of gold and the skittering script of the nerubians. Inside is a heart, gray with age but still very much alive. It beats slowly, as if dormant." Most of the Nerubian Archeology works refer to various unliving rituals. Necromancy. I'm just trying to show you that there are other possible explanations to nerubains having Necrolord-esque buildings at the time of Warcraft 3: Even besides the most obvious one being the Scourge just had them built.
Re-contextualizing existing lore is something that always happens to long franchises.