Could someone explain a little more about 'expiration continuing where
it left off' - this seems to imply to me that 'Cancel Proccess' on an
expiration causes the work the expiration has done to roll back,
whereas
'cancel expiration' does not?

Matt - Here's what we know about it, as noted in ADSM QuickFacts:

CANcel EXPIration                       TSM server command to cancel an
                                        expiration process if there is
one
                                        currently running. This does
NOT require
                                        the process ID to be specified,
and so
                                        this command can be scheduled
using the
                                        server administrative command
scheduling
                                        utility to help manage
expiration
                                        processing and the time it
consumes.
                                        TSM will record the point where
it
                                        stopped, in the TSM database:
this sets
                                        a restart checkpoint for the
next time
                                        expiration is run such that it
will
                                        resume from where it left off.
As such,
                                        this may be preferable to CANcel
                                        PRocess.
                                        This restartability was
introduced by
                                        ADSMv3 APAR IY00629, in
response to
                                        issues with long-running
Expirations.

A simple CANcel PRocess, on any process, serves only to terminate it.

   Richard Sims