Confirmed — and you were right to kill thousands, because it was never going to drop. Quest-conditional drops (items that only appear while you hold the quest) are a real mechanic and it was not implemented, so Gwin's Bag had no way to exist. That mechanic is now in and Iron Boars carry the bag while the quest is active. Leaving IN PROGRESS until you confirm a drop, since I could not test it in-world myself. Take the quest first, then hunt.

Closing this - Mark's v54 pass confirms Iron Boars drop Gwin's Bag while you are holding the quest.

You were not unlucky. 4031226 had NO dropper row anywhere in our data, so no number of boars could ever have produced it. "I have summoned and killed thousands of them to confirm" was measuring a drop table with nothing in it.

The dropper is sourced from the client's own quest data rather than guessed:
- Quest.wz Check.img 9321/1 wants npc 1022002 (Manji) and item 4031226 x1.
- Quest.wz Say.img 9321/1/stop/item - the line Manji speaks while you are on the quest - is "they do say the Iron Boars turn up in a hidden area".
- String.wz Mob.img 4230400 is Iron Boar.

It is a quest-conditional drop, the same mechanic as Cosmic's drop_data questid column, so it only rolls while quest 9321 is actually in progress.

Being straight about one thing: the CHANCE is unsourced. No server drop table we hold carries 4031226 at all - Cosmic, BeiDou, MapleSolaxiaV2 and JMSv186 all searched, zero hits - so the rate follows Cosmic's own convention for a one-off quest-gated item from a named dropper. If you turn up a real v83 rate, say so and it gets replaced.

LIVE on the published build.