Calculating Odds

When I want to calculate the odds that im going to hit certain cards, i use the rule where its 4% per card after the flop, and 2% per card after the turn. My question is this, lets say after the flop, you need a jack to make a straight. There are four jacks in the deck, so thats 16% chance of making the straight. However, at a 9 person table, 18 cards have been dealt out of the deck of 52 which is more than 1/4 of the deck. So chances are that one of the jacks have already been dealt out.
When you use the 4/2% rule to calculate odds, does it already compensate for the fact that some of your outs will already have been dealt out? Lets say someone's cards were dealt out and a jack was accidentally flipped up.... now when you calculate the odds, should you use three times 4% or still use 4 times 4%?

Outs are the cards YOU have not seen. The cards that the other players are holding are part of your outs (as they were unseen by you).