Complex sentence: In the Bardock special a younger Nappa is seen with hair, also note that Vegeta had long bangs like Goku, so it can be assumed that some time during their journey someting caused them to lose their hair.
Split into simpler sentences: In the Bardock special a younger Nappa is seen with hair. Also note that Vegeta had long bangs like Goku, so it can be assumed that some time during their journey someting caused them to lose their hair.