Exactly. They've already expired the payments to unclaimed royalties for people owed for '96-'00. If the people didn't register with SoundExchange by Dec of last year, it's too late to get thier money for that time period. '00 - Now is still claimable.
Read the Unpaid FAQ
Unpaid Artist List
Admittedly, most of the artists on there aren't people I've ever heard of.. but some of the names do ring a bell. Abraxas Pool, Blood Sweat & Tears, Cherry Poppin' Daddies are on there.

There's something like $50-60 mil outstanding to these people.
Oh, here's a fun sidenote for ya to think about: Instead of using ghost singers (ala
Milli Vanilli), ghost writers (you think bands have time to write, practice and record music while touring?) or lip syncing (lotsa names here), the recording industry came up with technology like
Autotune a while back that allows mixing software to correct the waveform of a singer's voice while they sing. In other words, they could sound half as bad as William Hung before the software and afterwards they'll sound like oh... Britney Spears. They've been using amazingly talented singers to sing a track as a guide for a B grade singer that looks like a million dollars on stage. The software corrects the B grade singer when they miss notes to the A grade's waveform or an established norm for the song.
Basically, if you think it's fake it probably is when it comes to things like MTV and the RIAA's artists. Looks > singing ability, because they can 'fix' singing ability now.
Edit: Oh yeah, and if you didn't see this already.. here's an old clip of
Enrique Iglesias singing.. kinda.