This was always confusing to me. In 1965 Motown released a 2-disk greatest hits package on the Miracles. Two years later they did the same for the Supremes.
Oddly, the followup Smokey Robinson & The Miracles package was label Vol. 2 in 1968. However, the follow up hits package on the Supremes in 1970 was labeled Vol. 3. Seems the Miracles 1968 set was also Vol. 3. What was up with this?