The source treats qāmā al-Zaydāni as weak or less standard relative to qāma al-Zaydāni: the preceding verb does not normally take a dual suffix when its full subject follows.
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The Less Common Dual Pattern
Feminine Tāʾ in the Past Tense: Form and Agreement
The source treats qāmā al-Zaydāni as weak or less standard relative to qāma al-Zaydāni: the preceding verb does not normally take a dual suffix when its full subject follows.