Are Johan and Juha different people?

All official documents in Finland were written in Swedish until late 1800's. The language of record applied also to names. A person called Matti would be recorded as Matts and a Liisa as Lisa or Elisabeth. And the same applied also to place names and family names.

How to record the names to your genealogy?

So there are 2 different schools who continue to disagree
1) those who record names as they are, in Swedish, but having to do some normalisation as the names are usually spelled several ways. So for example, unless you want to save space you could write the patronym in the full for Johansdotter even though in many records it is shortened.
2) those who feel it is more correct to record names in a Finnish form. If they read Pardain or Pardanen they record Partanen as that is the name today. First name Staffan can be recoded as Tahvo or Tapani based on what was the most common Finnish form of the first names based on the saint name Stephan in the area.

My personal preference is for the first in terms of first names because I can't claim telephatic skills to choose one of the many forms of for example Johan or Catharina in Finnish to be the "right" one. I feel more comfortable in normalizing the family names or farm names to the "modern" forms, as there is less/no guessing involved.

By the way, we still celebrate name days based on the old Catholic Saint calendar in Finland. (Additions have been made, though) So on Saint John's day in June men named Johannes, Juhani, Juha, Jukka, Janne, Juho, Jani, Jussi or Juhana are all honored. If they would have been born 200 years ago they would all be known in written documents as Johan. On November 25th, the day of Saint Catharine of Alexandria, among the name sakes are Katri, Kati, Kaisa, Kaarina, Kaisu, Riina, Katriina, all of whom could have been recorded as Catharina/Karin/Kaisa in church records, no matter what their families actually called them.