NWT Yumi dress size 6

NWT Black and floral Yumi dress. Bodice is lined, sleeves are sheer. I love this dress but it is too short for my chubby knees! Tag says size 2/4, another tag says size 6. UK size 10. It fits me - a 6/8. Measurements are 16 1/2" waist, 17 1/2" armpit to armpit, 23" sleeve, 32" long. Back zip.