Many thanks for your advice - not sure if this is standard for SIMS, but when I sort students for unprovisioning, as you suggested, by year I note that for some students the year group is in brackets, which appears to indicate student has left, which then makes it easy to unprovision these.
For "contacts to remove from provisioning" I can only see Name, Title, Address, Tel No. So far have found a way (convoluted) to get this list into excel so that I can sort it and then compare with a list of contacts for students on roll (extracted as a report from SIMS), and so intend to remove any contacts not on this latter list