Normally they announce the dates before og close to the current years races. So for a july 2020 races i would not expect dates before june 2019.

Many, many years ago, there was a calendar link at the bottom of Ironman.com that had all the dates for each race for the next couple of years. That's long gone and you typically cannot guarantee a future date until the current year's race is over and they've posted next year's date. Sometimes they will post next year's date immediately, and sometimes it takes several weeks or even longer if there is a permitting issue.