Are Sundown Subs Underrated on their RMS?

Pretty much what the title says. I see comments once in a while talking about how Sundown underrates their subs and how “you should put double the RMS on it to really wake them up”, and I’m wondering where this notion came from and if it’s remotely true. I’m not talking burps either - nor minutes of sine waves. I mean for playing bass heavy music, hip-hop, EDM, etc.

EDIT: Just wanted to say thanks for all the input fellas! Got 2100W on four SA V.3 8 inchers, didn't know if I could upgrade my amp in the future and hang on to them a little longer.. now I know!