It's been a long time since the Battlefleet Gothic Main Rulebook was published; almost 20 years! In this time, several magazines were published, a few books including the Armada expansion, the 2007 official update and the 2010 update that would have been official had it been published before GW discontinued Specialist Games.
...and in all this time, there's been one extremely obvious error that not even I, an anerrotypical obsessive neckbeard caught until today.
Behold! The entry for the Slaughter class Cruiser.

Red circle is mine. This is on my high-quality pdf that someone kindly made, but I double checked and it's in my hardcopy as well. It's not mentioned in ANY update I've seen.
I'm assuming that because the fire arc is Left that it's supposed to be a Port weapon, NOT a Prow weapon. Regardless, I think i'll play with it as a Port weapon, as does everyone else I've played.
However, I know that there are members of this forum that are a greater authority on this old chestnut than I am. I was hoping for the opinions of the revered gentry of the Specialist Arms Forums and the ruling of the more venerable members responsible for various official documents.