Okay, I'll try to explain this the best I can. So we all know (if you've seen the movie) that Skipper, Kowalksi and Rico adopted Private as their younger brother, so he's not their REAL brother so we can scratch Private out of this. Okay, so in the TV Show episode: The Trouble With Jiggles. Skipper says: "Anyone whose last name doesn't end in -OWALSKI have any options [to stop the jiggli]?" It is thus shown that Kowalski is actually Kowalski's surname. But does that mean that Skipper and Rico's last name are also Kowalksi. I think it could be but I also think it's not because Skipper uses the last name against him, making it seem like he is the only one who has that last name. So, we're Skipper, Rico and Kowalksi friends who became soldiers together? What do you think? Let me know!