TIER 1 JUNGLE ITEMS: Hunter’s Machete and Hunter’s Talisman grant 15 ⇒ 50 bonus experience on large monster kill
TIER 2 JUNGLE ITEMS: Stalker’s Blade, Skirmisher’s Sabre, and Tracker’s Knife grant 30 ⇒ 50 bonus experience on large monster kill
I mean, it's not specifically stated, but as RangerofShadows says, it makes sense they don't stack because the full-build items give the same amount as the smaller ones. It just doesn't make sense tome because each of the bonus exp lives inside of a unique passive with two different names.