Look beyond the pitcher to the leaf and you will see there is no distinct petiole. N. alata has a distinct petiole while N. ventrata is in between the strap leaf of N. ventricosa and the clear petiole of N. alata.
The other thing you need to realize is that for about 25 years now. Deroose has sold thousands and thousands of N. ventrata around the US at garden centers and home centers labelled as N. alata. They continue to do so today. http://www.derooseplants.com/en/sele...ntWebInfoId=59