I'm not very familiar with the the taxonomy of the Philippine nepenthes species and I don't grow N. sumagaya. I heard from friends who have visited N. pulchra habitat, that it's different enough but similar to N. petiolata. The difference is mainly the size of the leaves and pitchers and the bigger bulbous base.
N. petiolata line drawing:
N. pulchra in habitat
Sorry I couldn't be of more help regarding N. sumagaya.
The only other thing I know about N. sumagaya is that wistuba previously named it N. amabilis, but that name had apparently already been assigned to a hybrid involving N. ampullaria and N. rafflesiana, I recall wistuba been quite annoyed when cheeky Martin Cheek, who did precious little to discover the plant and played no real part in its description, but somehow on a technicality was able to name it whatever he wanted. It's a funny game this taxonomy business. Does anyone know where this list of "Binomial nomenclature" names exists? I'd like to be brought up to speed with any random names and descriptions that never materialised incase I ever want to name something.