I think yes, some “cultivated” plants can be hard to ID, and most Casual observations are hard to find. Also, some plants can be confused as planted if they grow too close to human settlements (and are not native or are common) such as the afrementioned Brugmansia. I believe that the RG for Casual ones can be really useful and is a great idea on itself.
But how could we determine the “casual”-ity of plants we find once, or cannot 100% confirm they were wild or planted? Take this, this, this and this as an example.
The first one: I know, it looks cultivated, but it was actually growing out of an old Tagetes garden left unattended. I got no answer if it was planted (and it had spread out to the wilderness!) so, is it candidate for RG?
The second one: Appears to be a large, old population that adapted well. Grows on abandoned gardens of a ranch alongside wild vegetation. I noticed that this part collides with forest so… is it candidate for RG?
The third one: I have strong suspicion that it belongs to the genus Pseudogynoxys, and more specifically, the Mexican Flame Vine (Pseudogynoxys chenopodiodes) which is ornamental. I suggested P. scabra for a nearby individual, but not sure. Furthermore, this is a recreational ranch, so… is it candidate for RG?
The last individual: Hymenocallis littoralis has no known local name and there are more populations in the park I took the photo in. These grow without any known order and are 10+ years old. That specific individual grows near the former place of a Spathodea campanulata tree. There are about 6 individuals, only that one and another reaching flowering size. As far as I’m aware, it hasn’t been considered as a ornamental in the zone (so no seeds spreading) and wild populations grow in riparian grasslands north of the village. Is it eligible for RG?
All of these are circunstantial. Do we know exactly why are these plants there? No. That’s why I believe RG and Casual should have a midpoint (other than Needs ID!) just in case.