O planeta natal era o mais distante (ou um deles de qualquer maneira). Eles demoraram mais para chegar ao planeta.
Navios mais novos foram enviados para planetas próximos, então eles tinham uma tecnologia melhor, mais caças, etc.
"And the ships have been traveling for seventy years--"
"Some of them. and some for thirty years, and some for twenty. We make better ships now. We're learning how to play with space a little better... The first ships we sent to the most distance objectives, the more recent ships to the closer ones. Our timing was pretty good. They'll all be arriving in combat range within a few months of each other. Ender's Game - Ch. 13