Dose the Halo time line make sense with the entry of halo wars into the time line?

IN halo wars the Spartans have shields but in the book the Spartans go to reach 20 years later for the final version of the armor that is equipped with shields that they got from reverse engineering covenant technology and that they also screwed up the story more with the addition of the Spartans in halo wars and a tone of other holes? I know that in the other books other Spartans are not present at reach because of covert secret operations and i just want to straiten things out in my head.