Tile Terrain Generation

I'm trying to create a terrain out of a grid of individual 4-vertex planes which will eventually be customized for different materials(i.e. clay, dirt, sand, etc). I am able to create a grid of flat planes, but when I try to alter the height of individual vertices, only the bottom left square(Tile00) renders and the remaining are instantiated as empties.

Here is my script. I can't quite figure out what's wrong, and I'm not getting any errors other than two variables not being used.

 using UnityEngine;
 using System.Collections;
 
 public class SpawnTester : MonoBehaviour {
     public GameObject board;
     public Transform tile_prefab_;
     public int board_size_x_;
     public int board_size_z_;
     public int nameX;
     public int nameZ;
     
     void Start(){
         GenerateTiles();
         GenerateHeight();
     }
     
     void GenerateTiles () {
           board = new GameObject();
           board.name = "Board";
         for ( int x = 0; x < board_size_x_; x++ ) {
              for ( int z = 0; z < board_size_z_; z++ ) {
                 Transform tile = (Transform)Instantiate(tile_prefab_,new Vector3(x * 10,0,z * 10),Quaternion.identity);
                 tile.name = "Tile" + x + z;
                 tile.parent = board.transform;
                
                 
             }
         }
         
     }
     
     void GenerateHeight () {
         for ( int x = 0; x < board_size_x_; x++ ) {
              for ( int z = 0; z < board_size_z_; z++ ) {
                 Transform tile = GameObject.Find("Tile" + x + z).transform;
                 
                 Mesh mesh = tile.GetComponent<MeshFilter>().mesh;
                 Vector3[] vertices = mesh.vertices;
 
                 if(tile.name == "Tile00"){
                     for(int i = 0; i < vertices.Length; i++){
                         vertices[i] += Vector3.up * Random.Range(0, 11);
                     }
                     mesh.vertices = vertices;
                     mesh.RecalculateBounds();
                     mesh.RecalculateNormals();
                     MeshCollider meshc = tile.gameObject.AddComponent(typeof(MeshCollider)) as MeshCollider;
                     meshc.sharedMesh = mesh;
                 }
                 else{
                     
                     int tempX = x - 1;
                     int tempZ = z - 1;
                     if(tempX < 0)
                         tempX = 0;
                     if(tempZ < 0)
                         tempZ = 0;
                     
                     string leftName = "Tile" + tempX + z;
                     string botName = "Tile" + x + tempZ;
                     
                     Transform leftTile = GameObject.Find(leftName).transform;
                     Transform botTile = GameObject.Find(botName).transform;
                     
                     if(leftTile){
                         Vector3[] leftVerts = leftTile.GetComponent<MeshFilter>().mesh.vertices;
                         Vector3 leftVertTop = leftVerts[0];
                         Vector3 leftVertBot = leftVerts[3];
                         vertices[1] = leftVertTop;
                         vertices[2] = leftVertTop;
                     }
                     else{
                         vertices[1] += Vector3.up * Random.Range(0, 11);
                         vertices[2] += Vector3.up * Random.Range(0, 11);
                     }
                     
                     if(botTile){
                         Vector3[] botVerts = botTile.GetComponent<MeshFilter>().mesh.vertices;
                         Vector3 botVertLeft = botVerts[2];
                         Vector3 botVertRight = botVerts[0];
                         vertices[3] = botVertRight;
                     }
                     else{
                         vertices[3] += Vector3.up * Random.Range(0, 11);
                         
                     }
                     
                     vertices[0] += Vector3.up * Random.Range(0, 11);
                     mesh.vertices = vertices;
                     mesh.RecalculateBounds();
                     MeshCollider meshc = tile.gameObject.AddComponent(typeof(MeshCollider)) as MeshCollider;
                     meshc.sharedMesh = mesh;
                 }
             }
         }
     }
 }