If the boards are Pressure-Treated wood, I'd replace them. I don't work w/cedar or otherwise to say what you should do, but I'd suspect the 'answer' is the same.
With PT wood, it will continue to 'bleed' for a while. What I've done in the past is, if the BOTTOM of the board is in good shape, I just use that side as the 'new' up-side (assuming the bleed isn't all the way through.) Knots are the worst! There, I've had to replace the boards because they went all the way through.
Be sure to let the board 'dry out' if it's new before you install it. Otherwise, it will shrink and possibly split on you.