It probably depends on the content of the record you are looking at, but, those can be two different names. The website Think Baby Names lists Fernan as a boy's name of Old German origin which means "ready journey". It is a variant of Ferdinand or Fredinando. Fern is usually a girl's name. I wonder if you could share a link to the record or a screen shot to get a better answer.
I dont see how one could make a blanket statement.
There surely must be cases where the names are not the same
(even if in some cases they are the same)
That being said - unless you have some clear additional indication
I think you would have to assume they MAY be different.
I have done a lot of German genealogy and find that many of the last names end with "in". Generally in regards to female last names. This seems to be most prevalent in pre 1800 records. For example, the name Link is common in my tree, but in early records was recorded as Linkin or Linken. I have found birth records with the "in" added and the same persons death record without it. I don't know the reason, just that it is common. My guess would be that it is the same name.