pre-washed vs. washed at the grocery store?

[blizzard of ahsss]

I bought a bag of carrots and a container of lettuce at the grocery store. The carrots say "washed" and the lettuce says "pre-washed." I know the carrots are ready to eat because they say "washed" but what about the lettuce? Do I have to wash it again?

If a pre-school is the little school before school, a pre-workout is a mini workout b4 the real thing, is a pre-wash the little wash before the main wash?