
I did not check your location Rayner. That could introduce a whole lot more possibilities into the equation.
I assume, since you have asked about Privet that you have them as weeds there as we do here. Your climate is probably similar to ours so autumn is the time these trees have berries that the birds eat and spread the seeds.
Personally, I think these are weeds and not worth the time for bonsai but they are hardy. They also shoot from older wood and can tolerate severe root pruning. That makes them good for collecting and good for beginners to practice with. You will learn a lot about how trees grow from this collection. It may even grow into a creditable bonsai but it will still be a privet

(

) larger leaves and stiff growth habit will be issues for you to deal with but with time and effort you could overcome those (maybe?)
Enjoy the experience with your yamadori privet but please get some trees that will produce real bonsai as well.