And then .... just to confuse us all ... later issues in the UK series (they went up to Volume 8 issued in January 1970) had radically different track listings from subsequent US issues (the US series went up to Volume 11 in September 1969). I'm looking forward to all of these compilations appearing on 45Worlds in due course.
Meanwhile, back in The States, they had their own series .. the first three were never issued in the UK but then in 1967 UK Tamla-Motown issued the US Volume 5 as their UK Volume 4 and the US Volume 4 as their UK volume 5.
Perhaps the Brit. Vol.1 of this series was a Britain/Europe-only release, the source company started their series and British EMI simply made the US Vol.1 into the British Vol.2, and so on down the line.(US Vol.2 = Brit Vol.3 etc.).