What about QUEST_TRACKER.tracked, can't you just loop through it to get the quest indices? Every quest appears to be added to it. Although there is a function to remove a quest from the tracker
Lua Code:
ZO_Tracker:SetTracked(questIndex, tracked)
it doesn't look like its used. There are a few checks to call it & remove a quest from the tracker if QUEST_TRACKER:IsFull(), but since:
Lua Code:
tracker.MAX_TRACKED = MAX_JOURNAL_QUESTS
I don't see how that would ever happen, unless some addon manually removed a quest from the tracker.