Dumb guard duty question

Ok, so I understand why guard duty won't give you the untap or +1 intercept if someone is trying to do a (D) action at your location at 0 stealth, as per the rule book. What I don't understand is how can vampires with +1 stealth and +1 intercept get those bonuses when they're not needed. Or, how someone with a Bowl of Convergence gets the intercept before it's need. Can someone explain this to me?

On Jan 5, 2:18 pm, devilwithcape [ quoted text not captured ] He doesn't add +1 intercept; he *has* +1 intercept. Those effects are "on" when the action starts. The rule prohibits adding more when it isn't needed -- it doesn't prevent existing stealth/intercept from coming along. See also hunting's default +1 stealth.

That makes sense. Thanks!.