The State department in 1981 reported
In January 1981, Honduran officials discovered a large cache of concealed arms intended for Salvadoran guerrillas, which included M-16 rifles traced to Vietnam. Smuggled arms have continued to be intercepted. ... On November 27, Honduran authorities discovered a guerrilla safehouse on the outskirts of Tegucigalpa. Two guerrillas were killed in the resulting shootout, including an Uruguayan citizen. Nicaraguans as well as Honduran were captured at the house, where a substantial arsenal of automatic weapons and explosives was seized. Incriminating documents, including notebooks which indicate recent attendance in training course in Cuba, were also confiscated. One of those arrested, Jorge Pinel Betancourt, a 22-year-old Honduran, told reporters the group was headed for El Salvador to join El Salvadoran guerrillas. Two additional guerrilla safehouses located in La Ceiba and San Pedro Sula were raided on November 29, and authorities seized sizable arms caches, explosives, and communications equipment. These arms may have been destined for use within Honduras.
In secret back channel discussions, Secretary of State Al Haig told Cuba's VP Carlos Rodriguez
We believe that the presence of Cuba in Nicaragua constitutes a threat to the continent, and in addition, we believe that the activity of Nicaragua in El Salvador likewise constitutes a serious threat. I can assure you categorically that we are in possession of comprehensive proof of such involvement. There isn't the slightest bit of doubt about it. It's a fact. We have photographs, documents, minutes of interrogations and "confirmations" by those interrogated. For this reason, I cannot agree with that which you are telling me. I am not saying that you have no right to say it. You have every right to say what you want to, but we also have a right to draw our own conclusions from the events as we see them. We have proof, and we are telling you about it.
But the clincher was what was found in Grenada in after the 1983 invation, as Reagan recounted in his memoirs
We discovered over the next few days that Grenada was far from the balmy resort island it was depicted as in travel brochures. Even more than we had realized, it was already a Soviet-Cuban bastion in the Caribbean. Grenada's neighbors had been right. We got there just in time. Grenada's new airport, with its nine-thousand-foot runway, had been designed not for tourism as Maurice Bishop claimed, but for refueling and servicing Soviet and Cuban military aircraft. The barracks used by the Cuban "workers" on Grenada contained enough weapons and ammunition to equip thousands of terrorists. In the Cuban embassy, we found hollow walls stuffed with more weapons, plus documents linking Grenada's Marxists to Havana and Moscow, including one letter sent six months before by a Soviet general to the commander of the Grenadan army that boasted Grenada could be proud of itself for becoming the third outpost of Communism in the New World - after Cuba and Nicaragua - and adding that soon there would be a fourth, El Salvador.
Our troops brought back this letter and hundreds of other documents proving that the Soviet Union and Cuba had been bankrolling the Marxists on Grenada as part of a scheme to bring Communism to the entire region. The program was just beginning in Grenada; it was intended to go all the way through the Caribbean and Central America. We took this storehouse of documents to a hangar at Andrews Air Force Base outside Washington and invited the press to examine it. Reporters would have found evidence of everything we were saying. But very few did.
I could go on, like talking about the documentation found in the Soviet archives themselves after the Cold War, but I think I've proved my point for all intents and purposes.