makes it quite clear that it is a new world, not a pre-existing one.
Indeed. The piece beamMe
dropped out of the middle of my quotes was where Saavik says:
Admiral, you've got to see this! There's new life -- a whole new world, a Genesis world -- !
But Kirk is past hearing or caring. He is huddled up against the glass, destroyed. Bones looks on, helpless.
237 EXT. SPACE
A spectacular look at Carol's planet being born!
It's clear that the intent was that the planet formed where the Reliant exploded. If it was meant to have been Regula, they'd have shown it.
Exactly, including the space lab being wrenched from orbit and dissolved.