For a time during the WCML upgrade works, there were regular diversions via Darwen, Blackburn, Clitheroe and the S&C. They only operated on Sundays, were mostly double Voyagers and most definitely did not stop for passengers at Darwen. Whilst it operated it was a very intensive service, with two northbound and two southbound per hour - on top of the hourly local service. I don't know what is the source of information about calling at Darwen, but they would all have had to stop at Darwen in at least one direction, awaiting its path through the single track sections either side. It seems highly likely that the WTT had trains calling at Darwen as an unadvertised operational stop, perhaps this is the reason for the confusion.