I just watched a YouTube vid about the DSC system and learned that the system uses all DSC-equipped boats as a relay chain to communicate with a shore station. Link is below, start at 8 minutes into the clip if you want to zero in on this info.

This makes a hand-held DSC-equipped VHF even more valuable as a rescue tool.... certainly for coastal sailors it's a "no-brainer" (knowing this) if deciding between whether to get a DSC-equipped VHF or a PLB. While PLB would be preferred offshore, the VHF would be my clear choice within 50 NM of the coast.

I bought a floating hand-held VHF unit with built-in GPS a few years ago, which I clip to my belt if I leave the cockpit underway. It's the most likely to bring local help (local = faster).