I don't know, Pinan Shodan has different stances, different arm position in a couple of places, two foot stomps that Heian Nidan doesn't have, a very marked change in tempo for the reinforced block on the way back, so that leans me to believe that while they are clearly both very similar to each other that their differences just go beyond variation among dojos; I think they are different katas but they're still both wonderful. Pinan Shodan is my tournament kata so I am partial to it though I learned Heain Nidan before. Now in terms of differences among dojos, let's look at the nukite on the way forward where the kiai is. Some people have their fingers totally straight as is taught in Shotokan while others bend their fingers in such a way that all four fingers are even with each other. That kind of difference I would chalk up to variations among dojos and would NOT consider that difference to be enough to make them be considered different kata. Plus I don't think there are any pinans that are like Heian Sandan. Not sure...