Spoiler Alert if you haven't read The Thursday War.

So I was reading The Thursday War when I realised something: in the multiple ship engagements, none of the Covenant ships ever have any shields, neither 'Telcam's forces or the Arbiter's. Not only that, they fire normal missiles at the Infinity instead of plasma weaponry. Now, I don't know if it's because they can't repair their weapons and shields, or because author Karen Traviss isn't well informed about Covenant ships. Anyone have an insight?