NZ Marine Biotech ($20M MC - High Growth Prospect), page-283

Companies can become public in two different ways, an IPO (initial public offering) which is extremely expensive, where they go from the ground up to become listed, everything new, or alternatively an RTO (reverse take over) where a private company can buy out a defunct company that is no longer trading, although the "shell" of the publicly traded entity still exists. So you can buy that shell, reinstate shares to be publicly traded and bingo, youre now on the Australian Stock Exchange for cheaper than what an IPO would have cost.

In this case, that was XTV (the company that traded from 2011 until 2016 before unlisting. Then in 2019 New Zealand Coastal Foods were looking to go public, saw the shell of XTV, acquiried it and changed everything (the ticker to NZS, the registry, etc).

Although with that, the previous companies that operated under the same ticker (XTV) stock history still exists of course. Which is what youre seeing in that graph. Hope that helps with any confusion.