Jehovah's Witness The Great crowd is seen in Rev 7 in white robes washed in the blood of the Lamb can this be?

If the blood of the Lamb representing a cleansed condition in the white robes ,if it only applies to the 144000 why are they seen washing their robes in it? obviously they are taking advantage of it and shouting out about their salvation and clothed in white robes which signify purity that only the blood of the Lamb could accomplish?If this application of the blood is doing this for them how can we conclude that the great crowd is not in the covenant that is validated by the blood of the Lamb?