They changed the wording of Last Whisper's Unique Passive to "40% Bonus Armor Penetration." Logically, this seems to mean a multiplier of 1.4 to any flat armor penetration that you have. But the hover-over description says that it's the same unique passive as the current Last Whisper, only with 5% more penetration.
Which one is it? If it's the latter, then I don't really understand why they buffed Last Whisper. I thought ADCs having significantly more crit and lifesteal were negated by having less armor penetration, and that makes sense, but now it doesn't.