So this one - the 0808 departure from Sheffield - was indeed a double 185.
However, there was confusion about what would happen at Manchester Piccadilly. (AIUI the train has to split at Piccadilly as there isn't the platform space at Manchester Airport for a full 6 car set at that point). The announcement at Sheffield was that the front 3 coaches would continue to Manchester Airport while the rear 3 coaches would terminate at Manchester Piccadilly, and this was backed up by the seat reservations being on the front set. But the conductor on the back set (where I was - it was pretty lightly loaded, which was lovely, though I suspect the front set was much busier!) was saying that in fact the rear set would continue to the Airport and the front set would terminate at Piccadilly. I didn't hang around to see what actually happened but if that's right, and nothing changes, there's going to be a lot of confused and frustrated passengers wanting the Airport but ending up in the wrong half of the train.