Many of the foreign cars in Australia were built locally in kit form to get around the high import duties. So they were locally given their own vin tag by the local distributor after the kit was assembled.
For example with Australian land rovers they had their chassis and engine numbers from the factory in England, then had another local vin when they were built locally and registered. Sometimes this was 2-3 years after the initial kit manufacture.
So, if no records from the local distributor exist, your best clue to when your 500 was made may be the engine number, assuming the engine is the original one.
Turin Distributors pty were the Fiat importers, I think they shut shop in about October 1973. The top plate looks like a 'lubrication advice' plate that they would have put on. At that time in the UK (when it was still possible to service your own car, due to their simplicity), a similar 'stick-on' was put on either by the manufacturer or as part of the PDI at the retailing garage. The reference number could be an internal sales number. I don't know what the bottom plate is, sorry.