I believe it would have been a 142. I've noticed that this service has been created too, although in reality, it is just two trains combined into one. I live in Retford on the Lincoln to Sheffield line. Trains usually go from Lincoln to Adwick via Sheffield and Doncaster. They then form a service to Sheffield, and from there form a service to Scunthorpe. At Scunthorpe, they form a service back to Lincoln. That is the usual diagram throughout the day.
Every Monday-Saturday, there is a peak time extra service from Sheffield to Retford. Before the timetable change, this was formed from the 16:15 from Adwick. It would arrive in Sheffield at 17:05, normally in platform 4) before waiting for 19 minutes, continuing on to Retford at 17:24. After terminating at Retford, the train then formed a service back to Adwick.
Since the timetable change, the 16:15 ex Adwick runs into platform 8. It then waits for the
Manchester Airport service to depart before continuing on to Manchester Piccadilly via the Hope Valley and Marple. The Retford service now
originates from Sheffield. Presumably, the service to Manchester used to originate from Sheffield, but for some reason, these services have now been split. Maybe it's due to the shorter time the ex Adwick train has to wait in Sheffield, and also because it gives the ex Manchester train (which, according to Realtime Trains by looking at the booked platform numbers forms the Retford train) a longer time between service to allow for late running, particularly important during the peaks.
That's my observation and prediction anyway. Hope that helps!
Ryan