Q: If the money will be coming in at a later stage won’t it then be included/calculated in the next Zakah anniversary anyway? Could you please clarify this?
A: You will still pay Zakat on the debt that is owed to you even if you will also pay Zakat on the same amount next time.
Zakat is paid on wealth every year. Zakat is not just paid once on a type of wealth i.e. if I have £10k with me for the next 10 years, then I will pay Zakat on that £10k for 10 years. The same principle applies here with money which is owed to you.