Hi David,
One way of telling original Eley made Wasps from Rothery's version is the smell - I kid you not! The old Wasps smell of solid engineering, while the newer versions don't have a smell at all. You'll probably find visual inconsistencies with the newer pellets too, while the old style all look and shoot the same. The late John Rothery once told me that he used the Eley name on his Wasps for as long as he could, which is why Eley continued to be printed on the tins long after they stopped making them.
This is turning into a real anorak thread, so I think I'll turn in for the night.
John