Spanish native here, confirming that RSA is the institution that sets the language standard.
But, people always deviate from it, though in my experience in word meanings and pronunciation, never in grammar to a degree that it become intelligible to another Spanish speaker.
The toughest film to listen to for me was "The rose seller"[1] (1998), took me like 10m to get my ear accustomed to their pronunciation.
So is the Andalusian accent from a Northern Spaniard like me, it's close to the prosody and speech of the US Southern accent. The first 20 minutes understanding Risitas were pure hell. But you get used to it in a few days.
It's like some American trying to understand the Scott/Welsh (can't remember now) sheperd not exposed to it. I'm pretty sure they could be used to it in less time than a week.
