At Hula Global, we allow a total of 2 new iterations and a limited number of corrections. That's because a new iteration happens when the information you have provided in the tech pack or comments needs to be changed, or you want to do something different from what had been agreed upon.
A limited number of corrections are made when what you have asked for is not provided by us according to your specification. No additional sample cost or courier charges need to be borne by the brand, and that's why it is important for us as a supplier to have all important pointers well-documented.