Mistake 1: “غُلَامِي has a kasra, so it is always genitive.”
Correction: That kasra accommodates possessive yāʾ; the noun can be nominative, accusative or genitive.
Mistake 2: “الْعَصَا never changes form, so it is indeclinable.”
Correction: It remains inflected; its case vowels are estimated.
Mistake 3: “Every noun ending with yāʾ follows the same rule.”
Correction: The source specifically means annexation to the first-person possessive yāʾ, not every final yāʾ.