I noticed that if you save the concept art pics that Team Ninja posted on the official site, you will see that they present such names:
pic_hwc_02_d (Ayane's one)
pic_hwc_03_d (Kokoro's one)
pic_hwc_04_d (Hitomi's one)
pic_hwc_05_d (Leifang's one)
pic_hwc_06_d (Tina's one)
pic_hwc_07_d (Lisa's one)
pic_hwc_08_d (Helena's one)
pic_hwc_09_d (Christie's one)
pic_hwc_10_d (Mila's one)
pic_hwc_13_d Momiji's one)
pic_hwc_15_d (Ryu'sone)
pic_hwc_16_d (Hayate's one)
pic_hwc_17_d (Eliot's one)
pic_hwc_19_d (Zack's one)
pic_hwc_20_d (Ein's one)
pic_hwc_22_d (Genfu's one)
pic_hwc_23_d (Jann Lee's one)
pic_hwc_24_d (Rig's one)
pic_hwc_25_d (Brad Wong's one)
pic_hwc_26_d (Bayman's one)
Like you can see there are at least 6 files missing ("pic_hwc_01_d" / "pic_hwc_11_d" / "pic_hwc_12_d" /"pic_hwc_14_d" / "pic_hwc_18_d" / "pic_hwc_21_d") that very likely correspond to the characters as listed by TN in the DLC pictures on the official site: so Kasumi should be the n.01, Sarah n.12, Pai n.13, Bass n.18, Leon n.21 and very likely exist also two pictures called "pic_hwc_27_d" and "pic_hwc_28_d" for Akira and Jacky.
I think that these files exist, otherwise TN would have used directly numbers from 1 to 20 in their names: maybe they could plan to release them inside an eventual future artbook or guide of the game?