The effect of a base power 4 counter or base toughness 4 counter overrides any existing effects that set that creature’s base power or toughness, as appropriate. Any existing effects or counters that raise, lower, or switch a creature’s power and/or toughness continue to apply to the creature’s new base power or toughness. Any base power- or toughness-setting effects that start to apply after the counter is placed on the creature will overwrite the counter’s effect. (For the rules-savvy, yes, this applies in layer 7b.)