The big fear at the time was that if the war escalated too sharply, the Soviets would respond by invading Pakistan, which was well understood to be the rear base and armory for the mujihadeen. The decision to send stinger missiles to the mujihadeen came after six years of aid to the mujihadeen, including about three years of overt aid after President Reagan publicly acknowledged the program.

The stingers were not the first anti-aircraft to be shipped into the country, the CIA and China had been importing various anti-aircraft weapons since the beginning. In fact, the 1983 budget of $50 million of US aid to the mujihadeen including a full $17 million allocated specifically for anti-aircraft weapons.

So I guess that what I'm trying to say is that the stringers were definitely important tactically, don't get me wrong, as they were by far the most effective anti-aircraft weapon used in the war, and the Soviets had previously been dominating the battlefield with seemingly invincible Mi-24 Hinds. In terms of an escalation though, the effect is somewhat overrated. Yes, they were easily the most overt demonstration of American aid, but it was already well known, both within Soviet intelligence and just to the public at large, that the United States/China/Britain/Saudi Arabia were using Pakistan to arm and supply the mujihadeen. The big fear was that too much escalation would push the Soviets to invade Pakistan, but by 1986 the war had already been escalated to a point without a Soviet response that it seemed a safe bet to escalate further.

The calculation made by the Reagan administration and the CIA was essentially that, if they haven't already invaded Pakistan, a few stingers won't be the tipping point. They were right.