Now correct me if I'm wrong, but didn't these long voyages take a really long time back in the day?? I know that 23 years is a stretch, but depending on different ports visited, and other "missions" taken on by the crew, it doesn't seem that hard to believe.
OR
This just popped into my head so if it doesn't make sense, let me know, what if during the time period we see when it picks up Richard, it's not under control of the actual Black Rock crew?? Perhaps they got ambushed by pirates or something, and took on the guise of the Black Rock crew. Might explain a few things, like why the proest clearly identified the guy buying Richard as Mr. Whitfield (or whatever) when he didn't need to so that the crew could cover their lies, why a proper English crew stopped to buy condemned men as slaves in the Canary islands, and why Mr. Whitfield was so quick to kill the slaves.