How do the regular and exceptional feminine duals differ?

The Dual Noun: Inflection, Maqṣūr, Mamdūd and Iḍāfah

• All feminine tāʾ is lost
• Ṭālibah only forms plural
• Khuṣyah always loses nūn
• Ṭālibah keeps tāʾ; special khuṣyah drops it