I hope this topic doesn’t also end up down the rabbit hole of confusion too 
Anyway, my best interpretation that I believe aligns with the guidelines is as follows; if a plant was initially planted and has re-seeded, the initial plant would be cultivated and the new plants wild. Vegetative reproduction is not as straightforward but I think the best rule of thumb would be if a plant vegetatively reproduces and if those parts were severed from the cultivated plant they would be able to survive (i.e. have their own root systems etc), I would consider them wild. A single bush that has grown in height/width throughout the years would still be considered captive. All of these examples are provided there was no human intervention (though the last is captive either way).
My point on vegetatively-reproduced plants may spawn some debate and there are reasonable arguments to be made for both sides. Unless an offshoot is detached from the mother plant it can be difficult to determine whether it has a sufficient root system or otherwise to survive.
Overall I wouldn’t stress it too much, follow the guidelines as close as possible and in fringe cases go with your gut. There are many captive plants being submitted as wild as every day so just being conscious and marking plants as such is a huge help.