1945 D Jefferson Nickel RPM FS501 re-punched mint mark
When I variety hunt or attribute I look for die markers or diagnostics to verify and confirm. Some varieties have little to no diagnostic marks published, so finding them can be a challenge at times, particularly with various die stages. Luckily PCGS CoinFacts has phenomenal photos that usually help. Variety Vista sometimes write out or has close ups of some markers/diagnostics.
Here is a 1945 D silver Jefferson with RPM FS501. Die markers include a diagonal die crack NW/SW at the top of Tom’s head, several die polish lines on the reverse and the mint Mark itself. This is a hard to locate variety in the Jefferson series
Die polish lines around mint Mark and below S
Die marks around D and ghost outline for D to the right of D, including the tail from lower right of D