This has been my concern too. On the Aurora 3 times I drew attention to the mislabelled options. Listed as Gluten free but clearly not, as a coeliac you can tell my look or smell if something is gluten free. Each time the head chef looked through the ingredients with me and each time there was a gluten containing element. Although there was an apology each time, I feel annoyed that it is often viewed as a lifestyle choice, or a fussy eater. I raised my concerns with head office and was assured this would be addressed.
On the Ventura two months later, I was twice given gluten containing meals in the MDR, again as my meal looked identical to the other meals on the table I questioned the ingredients, each time the chef confirmed they contained gluten. So it appears as though it makes very little difference if you only eat in the MDR.
There have also been a number of occasions where the waiter has taken my meal away at the serving station as they have spotted that it is not gluten free.
It has now come to a point where I am cautious about eating without checking and it has definitely impacted my opinions of P&O, so much so that I am now trying other cruise lines.