Mil-spec is an overused marketing term used to identify features on a rifle or specific part.
(I am guilty of using the term as much as anyone)
The true mil-specs for most of the AR family of rifles is not specifically available to the public, those specs are held pretty tight by Colt, FN, etc.
In my opintion the term "Mil-Spec" can be honestly used when describing features on a part or a specific feature on a complete rifle.
Examples:
Front sight base- Forged is milspec vs cast
Barrels - 4150 is milspec vs 4140
Lowers- 7075T6 forging is milspec vs cast
Barrels - chrome lined vs not
Finishing - hard coat anodized vs others....etc....
Truth is very very few of us (if any) will ever see all the Military Specifications for all the parts of the AR rifle system, to include dimentions, tolerances, materials, finishes, functioning, etc...