Some extra context for the curious: https://pdf.stafforini.com/parfit-1995-unimportance-identity.pdf
In the case of Riker v William, neither are the original at that point, but the one stranded was the "more" original, especially given he hadn't used a transporter in 7 (I think) years, while Riker continued as normal, dozens per month for years.
Again, they both still are William Riker. Just one is "more" original.
It's a real ship of theseus situation.