Those blank label pressings were in the possession of either the producer, or one of the band members, and were purchased by several collectors.
The matrix details in the deadwax are identical to the released / green label Wheel's 4 release. They were pressed at the same time, not after the fact.
There are certainly a lot more of them around as compared to the Wheels 4 label single. So I wouldn't pay too much for one, maybe $150 tops