Wow classic (TBC) spell API - required but not available

Many items have their additional attributes labeled under “spells”

"spells": [
      {
        "spell": {
          "key": {
            "href": "https://us.api.blizzard.com/data/wow/spell/21477?namespace=static-2.5.1_38644-classic-us"
          },
          "name": "Increased Block 14",
          "id": 21477
        },
        "description": "Equip: Increases your block rating by 14."
      },
      {
        "spell": {
          "key": {
            "href": "https://us.api.blizzard.com/data/wow/spell/23203?namespace=static-2.5.1_38644-classic-us"
          },
          "name": "Block Value 15",
          "id": 23203
        },
        "description": "Equip: Increases the block value of your shield by 15."
      }
    ],

The “spell” api is not published in the documents, and when I try to hit one of those URLs I get a 404. This makes it really hard to get a true view of the stats an item has on it.