Исправил, готово

AntiAirCraftGun/AntiAirCraftGun/FormAntiAirCraftGunCollection.cs

@@ -106,7 +106,7 @@ namespace AntiAircraftGun
             FormAntiAirCraftGun form = new();
             if (form.ShowDialog() == DialogResult.OK)
             {
-                if (obj + form.SelectedZenit)
+                if ((obj + form.SelectedZenit)==1)
                 {
                     MessageBox.Show("Объект добавлен");
                     pictureBoxCollection.Image = obj.ShowZenits();

AntiAirCraftGun/AntiAirCraftGun/Generics/SetGeneric.cs

@@ -38,18 +38,18 @@ namespace AntiAircraftGun.Generics
         public int Insert(T car)
         {
             if (_places.Count == _maxCount)
-                return false;
+                return -1;
             Insert(car, 0);
-            return true;
+            return 1;
 
         }
 
-        public bool Insert(T car, int position)
+        public int Insert(T car, int position)
         {
             if (!(position >= 0 && position <= Count && _places.Count < _maxCount))
-                return false;
+                return -1;
             _places.Insert(position, car);
-            return true;
+            return 1;
         }
 
         /// <summary>