so, basically the scenario is:
when King Cold and Mecha Frieza arrrive on earth in the beggining of the android saga, both Trunk and Goku are trapped/gone wathever and can't come in to help.
So, we have the rest of the Z fighters, Vegeta, Gohan, Picollo, Tien, Krillin, Yamcha etc...
King Cold, Frieza and the minions that came with them.
PS: I was always curious about what would've happened if neither Trunks or Goku could intervene