Yes. If you post a normal <500g parcel over the counter at a PO you will get a tracking number for that parcel on your receipt. You then need to add that tracking number to the ebay order details.   If you post a number of the <500g parcels over the counter at the same time you will either need to hope you get someone who knows how to add a post code to each one on the receipt (seems some say its easy as long as you tell them before they start and others say its not possible at all) or you need to come up with some other way to remember which tracking number goes for which parcel.

I think for peace of mind I will pay the extra 20c then at least the tracking numbers will be assigned automatically.