The plate on the buried ship was layered and thick, and it was built to be hit. What flies now is rebuilt from wrecks and from an incomplete memory of how that plate was made.
The Ship learns a faction's plate by eating that faction's wreckage. Combine plate is alloy and rivet, there to be thick. Collective plate is membrane and chitin, there to grow back. Dominion plate is stolen hull treated with void, and it drinks some of what lands. Confederacy plate is iron under brass, built to take a pounding and to show the pounding.
The difference is whether a hit leaves a scar or leaves a hole. Everything you have ever cared about is on the inside of that difference.