Just a quick note to say that legally, any content accessed under a CC license is so available in perpetuity.
There is little point changing observations or images published as CC to a closed license. Unless you significantly modify these, the originals will always be available under a CC license.
There was a bit of discussion on this is a separate thread on licensing: https://forum.inaturalist.org/t/can-someone-explain-licensing-to-me-please/2691/13