Also, Finnish is a hard language, even for Finns. I run daily into cases where I have absolutely no idea how it is in correct Finnish - sure, everyone understands my Finnish, but for example, how does "The team of Jokerit" go in Finnish "Jokerien joukkue"? "Jokereiden joukkue"? "Jokereitten joukkue"? Is some of them wrong? Why?
Had to check this up and seems they are all correct and used. The "-den" and "-tten" are essentially the same thing but to my ear "-den" is the more official sounding one and I'd use it if I was writing a book or reading the news on TV. The "-tten" sounds like dialect to me and I think it's mostly used when speaking - not so much in writing. Personally I use "-den" exclusively.
The "-ien" suffix then again is the same thing as "-den" and "-tten" but used with the words where the other two doesn't work
I don't know the grammar behind this and too lazy to find out but words like "Viinit", "Viinien" (Wines) or "Sukat", "Sukkien" (Socks) only works with the "-ien" suffix and on the other hand words like "Tietokoneet", "Tietokoneiden/-tten" (Computers) or "Lentokoneet", "Lentokoneiden-/-tten" (Airplanes) only works with the "-den" or "-tten" suffix.
As said I don't know the grammar rules for this. I'd guess "Jokerit" is a rarity since all those suffixes sounds correct on it, at least to my ear