The ASA upheld a single complaint against the ad from the pro-Sudanese government group, the European Sudanese Public Affairs Council, which challenged the number of people killed. It claimed it was less than 400,000.
The coalition stands by the figure and says that it could be higher. However, it can not verify it because of access restrictions put in place by the regime in Khartoum.
The coalition said: "Essentially, the ASA has agreed that the scale of killing in Darfur to date could well be 400,000 persons, or even greater. However as a matter of absolute fact, this cannot be verified because of the ongoing actions of the Government of Sudan, which refuses to allow the international community -- including diplomats, journalists and humanitarian organisations -- access to the Darfur region."
However, the Advertising Standards Authority has denied that it "essentially" agreed with this figure and said that it was opinion not fact, but did not rule out that it could be true.
The ASA added that it did not want to quibble over what was a catastrophic figure, whatever the exact number, but said that its rules were about being able to substantiate claims.
The Save Darfur Coalition said that it accepts the ASA's ruling that the ad should have been qualified as opinion, but remains firm in its belief that "the scale of this atrocity is of this magnitude".
The coalition added: "History tells us that the scale of genocides is rarely accurately understood contemporarily. The international community must maintain the strongest possible pressure on the government of Sudan to have international peace keepers in Darfur as soon as possible to stop ongoing violence and end the killings once and for all."