Your example seems like maybe independent invention....
Given that mainstream music for the last number of generations has been essentially played on the same instruments, and following the same musical theory, one must come to the conclusion that everything has been played before.
Suggesting that someone plagiarized another's music without being able to show that they were exposed to the previous authors material is dicey business.

More likely is that both Elvis and Wagner caught that riff from someone else and incorporated it into their own pieces.

__________________
On some nights I still believe that a car with the fuel gauge on empty can run about fifty more miles if you have the right music very loud on the radio. - HST

1983 300SD - 305000
1984 Toyota Landcruiser - 190000
1994 GMC Jimmy - 203000

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