I would suggest initially that it worked into Dalmuir as a 6-car unit, which would be needed on a peak time service across Glasgow. I'd assume that at either Springburn or Dalmuir again one of the units will be detached and work a later service, or run back empty to Yoker and await further duty / maintenance.
Basically it's just that it worked as a 6-car before on a peak service and doesn't lose the extra unit(s) until after the service.