Generally credit is stated on your entry form, the quilt label often is something more personal or some shows want a minimum on the label, like name of your quilt, your name, city and state; but the other information is on the entry form. If someone sees one of their designs and questions the entry form can be obtained and shown the information.
A show organizer once told me they did it that way because often the people looking would zero in on the designer name and not acknowledge the person who made the quilt or worse would judge harshly believing it was not up to that designers standards.
Im sure every show is different and has their own rules. I don't generally put the designers name on my labels but I do include it in the quilt description