Agent 2276**LW was made in 1967.
The numbers started out that year at 220000LW, and ended that year around 345699LW.
The Pre-1972 unshrouded aluminum Colt's were NOT rated for ANY +P ammo.
It wasn't until the introduction of the heavy, shrouded barrel models in 1972 that Colt rated the aluminum guns for any +P.
Starting at that time, Colt first rated the aluminum guns for "UP TO 1500 rounds" of +P ammo before the gun needed a factory inspection, and "possible" frame replacement.
Later, in the 1990's Colt altered this standard to "inspection every 1000 rounds" with no upper limit.
In fact, many users of the older aluminum guns practiced with standard .38 Special ammo, and loaded the gun with +P ammo for "business".
Firing a small amount of +P ammo will not do appreciable harm, but any extended amount will cause rapid wear.
So, shoot standard .38's, carry with +P, and only shoot them when your least problem is increased wear to the gun.