Hi there,
There are certainly pictures of more than one tram standing in the yard at Upwell and, if I remember correctly, a passenger tram passing a goods service at either Boyce's Bridge or Elm Bridge. I've seen the operation of the Wisbech and Upwell described somewhere as a 'shuttlecock service' - I don't know what was meant by that but I would assume that, in the middle of a busy fruit season, more than one tram at any time could proceed down to Upwell, perhaps in a similar way to which a conventional train could follow another through a single line section once the first train had cleared that section. This may be too elaborate but I'm given to thinking the S&D followed a similar principle on busy summer Saturdays - through trains one way in the morning, back the other way in the afternoon or something similar.