Unofficial Skyrim Special Edition Patch

Based on my experience with this issue with the radiant quests in A Tale of Blood and Snow, you basically need to blacklist each no-reset dungeon individually. I’ll need to find what dungeons meet the requirements for this quest but can’t reset.

For some reason I made a list a long time ago with information about the different dungeons in the game (including their respawn settings), so maybe what I've listed below will be of some help.

From what I can tell, there are two specific conditions for MGR20, MGR20B, and MGR21.

(1) The location must have the keyword 'LocTypeDungeon'
(2) The location must have a reference type 'BossContainer'

The following no-reset dungeons meet the two conditions above, but I wouldn't be surprised if a few of them are already excluded by some other means (especially those that are only used for specific major quests).

Spoiler:

Altar of Thrond [DB]
Ashfallow Citadel [DB]
Blind Cliff Cave
Broken Oar Grotto
Cracked Tusk Keep
Dustman's Cairn
Folgunthur
Frossel [DB]
Frostmere Crypt
Gallows Rock (USSEP made this a no-reset dungeon to fix problems with the Companions questline)
Geirmund's Hall
Glenmoril Coven
Gyldenhul Barrow [DB]
Harmugstahl
Highpoint Tower [DB]
Hillgrund's Tomb
Ironbind Barrow
Kolbjorn Barrow [DB]
Mistwatch
Nchardak [DB]
Northwatch Keep
Ragnvald
Saarthal
Snow Veil Sanctum
Southfringe Sanctum
Stillborn Cave
Vahlok's Tomb [DB]
Valthume
Yngol Barrow
Yngvild
Ysgramor's Tomb

The following no-reset dungeons don't meet one or both of the conditions listed above, so it's pretty safe to say they can't ever be chosen.

Spoiler:

Angarvunde
Arkngthamz [DG]
Avanchnzel
Bthardamz
Darklight Tower
Forebears' Holdout [DG]
Irkngthand
Japhet's Folly
Kagrumez [DB]
Karthspire
Korvanjund
Labyrinthian
Mzulft
Nightcaller Temple
Nilheim
Rannveig's Fast
Reachwater Rock
Ruunvald Excavation [DG]
The Katariah
Tower of Mzark
Twilight Sepulcher
Ustengrav
White Ridge Barrow [DB]
Wreck of the Icerunner

Shouldn't setting the Allow Cleared flag appropriately be enough to cover all cases? I pay very little attention to the flag but surely it won't be removed from a dungeon that never resets?

Description from the Creation Kit wiki:

Allow Cleared: If unchecked, "Cleared" Locations will never be selected for this alias. If checked, "Cleared" Locations can be checked, but uncleared locations will be preferred if available.

Purpose: This flag is useful in scenarios where you want to allow a quest to continue even if a specific location has been cleared, potentially for procedural generation or other quest-related reasons.

A Location Alias will not fill with a location that is cleared, unless the “allow cleared” flag is set (and even then non-cleared locations are preferred). Note: Forced Location Aliases ignore this.

The term "cleared" is a bit misleading because any location that has been cleared will show as such on the world map for the remainder of the game. I'm gathering that this isn't actually how the game detects its status. Instead it must check to see whether the location has reset. If that's true, then yeah, you'd think a non-resetting dungeon wouldn't ever regain that status.

Urag's book quests don't seem to have the "Allow Cleared" flag set on the alias condition that chooses the location.

As a comparison, the Treasure Hunter quests (WE100) don't have that flag checked either and they also send you to dungeons to retrieve an item from a boss chest. Strangely, I don't recall ever being sent to a location (to retrieve the enchanted weapon) that didn't reset and had previously been cleared. Though unlike with the book quests, these require there to be a dungeon boss.

Anyway, you guys would understand how all this works far better than me. I just wanted to make some notes based on some of my testing in the game and the information I've gathered, in case it might be helpful.