All instances of a prefab effected by single access -- no Static variables

I'm really at my wits end with this. Sunk a bunch of time into figuring out how to access a variable attached to an object that was a child of a child. I've got some treasure chests that are supposed to open when I 'ping' them from a second script. I figured out how to access the script, but now all of the treasure chests open with one click which I don't want. I have not declared any static variables, but its as though I'm using some kind of implicit static declaration. I can't find anything unusual assigned in the inspector. Here's the code from the animation script:

 using UnityEngine;
 using System.Collections;
 [RequireComponent(typeof(Animator))]
 //[RequireComponent(typeof(SonarcursorScript))]
 
 public class TreasureControl : MonoBehaviour {
 
     public SonarcursorScript sonarcursorScript;
     
     public GameObject TreasureLight;
 
     Animator anim;
 
     // Use this for initialization
     void Start () {
         
         anim = GetComponent<Animator>();
         anim.SetBool ("open", false);
         TreasureLight.renderer.enabled=false;
         GameObject sub = GameObject.Find ("Sub");
         sonarcursorScript = sub.GetComponentInChildren<SonarcursorScript>();
             
     }
     
     // Update is called once per frame
     void Update () {
 
         if (sonarcursorScript.boxInt == 21)
  
         {
             anim.SetBool ("open", true);
 //            Debug.Log ("This is it  "+sonarcursorScript.boxInt);
             TreasureLight.renderer.enabled=true;
             
         }
     }
 }

and relevant code from the calling script:

 using UnityEngine;
 using System.Collections;
 
 public class SonarcursorScript : MonoBehaviour {
 
     public int boxInt = 0;
     public string sonrTarget = "helpme";
 
 void Update() {
 if(sonrTarget == "Box") 
 boxInt =21;
 
 }

When boxInt is passed as 21 to TreasureControl.cs, all my boxes animate at once. They were all instances of the same prefab. Breaking the prefab instance did not fix it. Changing the instantiation method didn't either. I'd appreciate any help. Thanks!