How is Zakat calculated when trading goods (Urood) are acquired at separate times?

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If one possesses trading goods acquired at different times, they are not aggregated with prior possessions because acquired items do not join existing holdings to complete the Hawl (one-year period). However, if the initial holding was less than the Nisab (statutory minimum), and the second acquisition completes the Nisab, the Hawl for both begins from the time the second acquisition was made, and any subsequent growth follows that date. A third acquisition does not combine with the first two; its Hawl begins from the time it is acquired. Zakat is obligatory on this third acquisition if its value reaches the Nisab, even if it is less than the Nisab on its own, because the prior holdings already constituted a Nisab, meaning Zakat is due proportionate to its share, and its growth is consequent to that basis.