AFAIK the second are lowers. to be a TRUE upper pitcher it has to have a loop. ive seen exceptions though with plants like N. inermis that dont curl. the reason for the loop is so it can grab on to twigs and branches so it can support the vine. as stated N. veitchii has its own way of overcoming this by wraping the leaves around trunks of trees.
I have several "true" uppers right now that don't curl. Most do, however. N. truncata doesn't have prehensile uppers either for example.