having worked for a major manufacturing company, what they will make under their brand name and what they make as a store brand will be slightly different. it is possible that the robert kaufman branded kona is made with a different cotton quality, higher thread count, denser thread, etc. the non robert kaufman branded kona in joann's is probably made with lesser quality materials.
i know my company put out different store branded or private label branded products than their branded products. their branded products included much better ingredients in higher concentrations. just a thought.