I think it depends entirely on the integrity of the cremator. I have a good friend who does pet cremations. He cremated one of my pets and told me that he had a hell of a hard time getting the bag of ashes into the box I gave him. I laughed and asked him why he didn’t just pour some out so the bag would fit more easily. Who would know? Who would care if there were a few grams missing? Especially if the reason was that the client-provided box was too small. But he was genuinely shocked and said he would never do that.