Giant Harpoon - Stacking with Isarnia

Is the Giant Harpoon Def nerf stacking with Isarnia’s special or with one of the Ramming Pulverizers?

Linking this back up because no-one answered. I’m not sure what ‘nerf stacking’ means… but do Issie and the Pulverisers stack with the GH?

it doesnt. the latest def debuff overwrites the previos one.