I could be wrong, it's been a while since I read Ender's Game completely, but didn't they say that we first knew of the Formics because of an attack on a family miner's ship? This is covered in Earth Unaware but they blast the Italians ships to bits and I remember that in Ender's Game they show the first attack in a video as the Formics slaughtering them unaware of being recorded(as they had no need for recording)?
enders game just brushed on the beginnings of meeting the formics, anything said in Enders game, but then doesn't quite fit in newer books are simply because card is elaborating in the newer books. And from what I've read, Ender's Game actually has newer editions now that fix some of these issues. Something simple like instead of the first time we meet the Formics to one of the first times, fixes simple little discrepancies like that.
This (discrepancy resolution idea) is covered in detail here: What is Orson Scott Card's position on discrepancies between various Enderverse books?