"Record Locator" is basically equivalent to "PNR". They are interchangeable.
"PNR" is an abbreviation of "passenger name record".
However AA use SABRE for their GDS (booking system) while Qantas use "Amadeus".
When there is a reservation ticketed by QF with AA flights or vice-versa there will be both QF and AA "Record Locator"/"PNR"'s - they will almost certainly be different.
Having posted that we are referring to an AA reference and they need to sort this issue out.
FWIW, USair used "Shares" - that's what the original PNR would have referenced before last weekend.