Actually, for the moment, there are 4
Nacaduba in the official Singapore checklist. There are probably at least 4 more which I have specimens of, but yet to properly catalogue and assess with the help of Dr Kirton, as there are other more urgent species to ID and I have to acknowledge that he's a busy man on the other side of the Causeway.
I know you mentioned that C&P4 is sometimes an irritation to refer to, but it's the best reference that we have. As I am outstation now, you may want to check the ID key for the Nacaduba in C&P4. Take a look at the checklist's 4 species, as well as the following, which I currently have only about 50% confidence of the ID of the specimens.
- Nacaduba pactolus odon
- Nacaduba subperusia lysa
- Nacaduba kurava nemana
- Nacaduba augusta kerriana