On the face of it, there appears to be little practical difference between an IPC and an instrument rating test. The two flight Test Forms appear almost identical.
If, for example an A320 pilot returning from overseas but not currently employed by an airline or operator in Australia, wishes to renew his instrument rating well within the normal 12 month expiry date, is he required to complete an instrument rating test or an instrument proficiency test? Where is the reference for this?