A complicating factor in many of the supply chains is that Coles and Woollies sell a percentage of their shelf space via a lease arrangement direct to the suppliers. (Well they used to and haven't seen anything to say the practice has changed) . Similar to Myers and DJs selling floor space to "labels" who fitout, stock, staff, and operate the floor space separately to the main department store.
The suppliers have to stock their rented shelves themselves. The supermarkets are not involved in supplying, warehousing, delivery, stocking shelves, stock turnover, merely handling the sale. I presume the suppliers get an electronic update nowadays overnight or some other period to tell them what was sold. They then make an independent decision on when to send stock and a staff member to each store to do the shelving independently.