JNA was stocking up for decades, 1st because of prospects of open war vs. Soviets and their satelites from late 1940s, then beacuse they regarded NATO as a threat. That is more than 40 years of making warehouses, filling them up to the brim with guns, ammo, food etc, then making new warehouses and filing those. Leadership of the JNA was probably happy to have some of the 1950s and 60s vintage ammo being used up against Croat forces in 1991. Basically - they lost just a portion of what was in warehouses.
What they needed by 1992, and what especially the Serbs in Croatia and Bosnia were short of, was manpower - someone to receive a rifle and to serve as infantry. Front lines were very long, and artillery and tanks are not that good in covering the hilly and forested terrain. With Slovenia and Croatia going away in 1991, and B&H and Macedonia following suit, Serb forces all around still have the same problem as it was the case historically. The Kosovo Albanians will not cut it, even for the forces from Serbia proper.
War in Croatia also teached the Serb forces some important and valuable lessons.
Lack of manpower in Serb forces was a key for survival of B&H, and one of reasons why the SAO Krajina folded up in 4 days. It almost cost the Bosnian Serbs their Republic in 1995.