Which general principle is correct for possessive yāʾ examples?

Iḍāfah to Yāʾ al-Mutakallim and the Six Nouns

• Every mudāf is overtly genitive
• Yāʾ is mudāf ilayh; the mudāf has its own case
• Yāʾ is always a subject
• Mudāf ilayh is a past verb