Smokey's Power Secrets gives that impression when discussing synthetics, that the synthetic basestocks are eternal, and just need additive replenishment...I put that down to the emerging knowledge at the time, rather than fact.
The local tech agent for Wynns back in the early 90s was running M1 5W-20 (IIRC at the time), but was using a bypass filter, Oil analysis (Wynns obviously did it), and was re-additising his oil on a perpetual oil change.
Removal of conatimants (bypass filter), top-ups, and monitoring, he probably could have gone perpetual without the adds.