I made a few images that point out the ID features for the Six Line Nacadubas and also a couple of easily mistaken species. Could you take a look and see if I missed out any important features? Thank you!
3. N. calauria. Dark striae strong in both sexes.
Female upF patch violet blue.
4. N. beroe.
Male with the dark striae weak & may be partially obsolete.
Wingbase darkened in the male.
Female UpF patch violet blue with bluish white submarginal spots.
5. Ionolyce helicon.
Not sure if the sub-basal bar is relevant.
6. Prosotas aluta.
Submarginal spots are not sagittate, but roughly lunulate.
FW postdiscal is usually described as dislocated at vein 4, with the lowest spot (in space 3, ie spot 3) shifted inwards.
Note; The space you marked as space 3 is actually space 4. Count the spaces from bottom up, ie. space 1b, space 2, 3, & 4.
Thank you Dr Seow for the corrections, especially the correct phrasing for the submarginal spots! I wanted to make it easier for more people to ID the Nacadubas and chose the more prominent features, since usually the uppersides aren't as easily observed, I did not put much emphasis on that. The darkness of the striae can be rather subjective and for less experienced shooters may be difficult to judge. Also the sub-basal bar in Ionolyce helicon was just an additional feature to differentiate it from Prosotas aluta, as some individuals do end up looking very alike, but I guess it could be omitted.