Thanks for the quick follow up and the USEP link. I've been using USEP (very frantically) for a good while now. Lol. Problem is I played Orsinium when it first came out. Completed the MQ & did some 99% of the side/free roam quests years ago. So that's why this has been so damned hard to get this achievement completed few years later. I literally had to parse the Wrothgar quest list on USEP and track down NPCs/objects where they were (or were not) supposed to be based on quest completion or not.

btw: you DON"T need to complete Maelstrom on either level to earn this achievement. This is just heads up for PvE non Arena/Trial focused ppl like me who's rather be off questing v. survival minigames in an arena.

Took me 6 hrs to finally find 3 independent side quests I didn't realize existed lol. So now I just got the Museum curator's final quest to unlock the costumes. ZoS really went to great extremes in hiding away NPCs when they created this DLC zone. >,<

^^
Yeah. I did this. But as mentioned missed a not so obvious quest (the one where you need to help out that total fail of a Dark Elf adventurer stuck in a dragur tomb). Easy to miss as the Orc village is really just a small rag tag band of anti Kurog outcasts living outside a ruin. And if you're not close enough to the Orc NPC female (or the Nord NPC who's his assistant just outside the tomb), you won't see the quest icon on the navigation bar. Anyhow it turns out that quest spans multiple DLCs (i.e. goes from Wrothgar to Morrowind etc). So made mistake of tracking him to other DLC zones. Only to find out it didn't count lol.

And the other missing ones were totally off the beaten path. e.g. helping that Artist Bosmer in the museum. This one was the perfect example of how you can miss out on doing side quests when NPCs can spawn in different locations (depending on where you're in the MQ story). So again if you're not within the NPC's vicinity (which toggles their quest icon visibility in the HUD nav bar) when at the Orc stronghold, then you're likely going to miss ever encountering him. That particular NPC hangs out at either the stables or inside the tavern. And respawns inside the museum for a final cutscene if you've completed the quest. Then permanently de-spawns from the game afterwards. So even if I HAD completed that quest years before, I'd never be able to verify if I'd done this quest earlier for achievement purposes. Because unfortunately, this particular quest was designed to spawn the quest NPC in several locations. Then permanently remove said NPC from game after you complete it >,<