Assassin Items - "Unique" Lethality - Does it apply to all items?

"Lethality" is a stat (basically flat armor pen) that can be gained from items, runes, and even a mastery. But in the patch notes the Assassin items have an ability called "Lethality" which gives, of course, some amount of Lethality. These abilities are unique passives - but not all Assassin items give the same amount (most give 15 Lethality while Ghostblade gives 20).

Simply put, does the "Unique" simply mean that if you have two of an item (e.g., two Ghostblades) the Lethality won't stack or does it mean that you can only get Lethality from one item, period (e.g., if you have Ghostblade and Duskblade you'll only get the 20 Lethality from Ghostblade, rather than 35 total)?