According to an article in The Guardian dated 8th September, the issue is that not all constitutions define their head of state the same way. In some cases, the hereditary monarchy is written into the constitution in such a way that King Charles III became head of state as soon as Queen Elizabeth II died, as he did in England and Scotland, but others have a less clear definition:
In many cases their constitutions state that the Queen, specifically, is the head of state. In these countries, constitutions will need to be amended to refer to her successor.
In many cases, the power of the monarch is to appoint a Governor General, who then acts as "the representative of the Crown". In such countries, the constitution may need to be amended to recognise Charles III as having power to appoint (or confirm the current appointment of) such a figure.
That leads to two things:
- Firstly, a delay as the necessary laws are drafted, and either parliament or entire electorates approve them.
- Secondly, movements within those countries to become republics have a chance to draw attention to their views, and argue for a referendum on that instead.