The book calls ʿAbd Allāh fully declinable, yet «عَبْدُ» has no tanwīn. There is no contradiction.
Rule: Being a muḍāf blocks tanwīn even if the noun is fundamentally triptote. Standalone «عَبْدٌ» may take tanwīn; in «عَبْدُ اللَّهِ» it cannot.
Absence of tanwīn alone does not prove a noun is diptote.
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Diptote Causes — Compounding and Its Conditions
The book calls ʿAbd Allāh fully declinable, yet «عَبْدُ» has no tanwīn. There is no contradiction.
Rule: Being a muḍāf blocks tanwīn even if the noun is fundamentally triptote. Standalone «عَبْدٌ» may take tanwīn; in «عَبْدُ اللَّهِ» it cannot.
Absence of tanwīn alone does not prove a noun is diptote.