diff --git a/src/upgradeable/ERC721CommonUpgradeable.sol b/src/upgradeable/ERC721CommonUpgradeable.sol
index f664fa6..3a7e70a 100644
--- a/src/upgradeable/ERC721CommonUpgradeable.sol
+++ b/src/upgradeable/ERC721CommonUpgradeable.sol
@@ -13,6 +13,7 @@ abstract contract ERC721CommonUpgradeable is
   error ErrInvalidArrayLength();
   error ErrNonExistentToken();
 
+  /// @custom:oz-upgrades-unsafe-allow constructor
   constructor() {
     _disableInitializers();
   }
@@ -20,22 +21,9 @@ abstract contract ERC721CommonUpgradeable is
   /**
    * @inheritdoc IERC721State
    */
-  function stateOf(uint256 _tokenId) external view virtual override returns (bytes memory) {
-    if (!_exists(_tokenId)) revert ErrNonExistentToken();
-    return abi.encodePacked(ownerOf(_tokenId), nonces[_tokenId], _tokenId);
-  }
-
-  /**
-   * @dev Override `ERC721Upgradeable-_baseURI`.
-   */
-  function _baseURI()
-    internal
-    view
-    virtual
-    override(ERC721Upgradeable, ERC721PresetMinterPauserAutoIdCustomizedUpgradeable)
-    returns (string memory)
-  {
-    return super._baseURI();
+  function stateOf(uint256 tokenId) external view virtual override returns (bytes memory) {
+    if (!_exists(tokenId)) revert ErrNonExistentToken();
+    return abi.encodePacked(ownerOf(tokenId), nonces(tokenId), tokenId);
   }
 
   /**
@@ -51,17 +39,6 @@ abstract contract ERC721CommonUpgradeable is
     return super.supportsInterface(interfaceId);
   }
 
-  /**
-   * @dev Override `ERC721PresetMinterPauserAutoIdCustomizedUpgradeable-_beforeTokenTransfer`.
-   */
-  function _beforeTokenTransfer(address _from, address _to, uint256 _firstTokenId, uint256 _batchSize)
-    internal
-    virtual
-    override(ERC721NonceUpgradeable, ERC721PresetMinterPauserAutoIdCustomizedUpgradeable)
-  {
-    super._beforeTokenTransfer(_from, _to, _firstTokenId, _batchSize);
-  }
-
   /**
    * @dev Bulk create new tokens for `_recipients`. Tokens ID will be automatically
    * assigned (and available on the emitted {IERC721Upgradeable-Transfer} event), and the token
@@ -73,17 +50,42 @@ abstract contract ERC721CommonUpgradeable is
    *
    * - the caller must have the `MINTER_ROLE`.
    */
-  function bulkMint(address[] calldata _recipients)
+  function bulkMint(address[] calldata recipients)
     external
     virtual
     onlyRole(MINTER_ROLE)
-    returns (uint256[] memory _tokenIds)
+    returns (uint256[] memory tokenIds)
   {
-    if (_recipients.length == 0) revert ErrInvalidArrayLength();
-    _tokenIds = new uint256[](_recipients.length);
+    uint256 length = recipients.length;
+    if (length == 0) revert ErrInvalidArrayLength();
+    tokenIds = new uint256[](length);
 
-    for (uint256 _i = 0; _i < _recipients.length; _i++) {
-      _tokenIds[_i] = _mintFor(_recipients[_i]);
+    for (uint256 i; i < length; ++i) {
+      tokenIds[i] = _mintFor(recipients[i]);
     }
   }
+
+  /**
+   * @dev Override `ERC721Upgradeable-_baseURI`.
+   */
+  function _baseURI()
+    internal
+    view
+    virtual
+    override(ERC721Upgradeable, ERC721PresetMinterPauserAutoIdCustomizedUpgradeable)
+    returns (string memory)
+  {
+    return super._baseURI();
+  }
+
+  /**
+   * @dev Override `ERC721PresetMinterPauserAutoIdCustomizedUpgradeable-_beforeTokenTransfer`.
+   */
+  function _beforeTokenTransfer(address from, address to, uint256 firstTokenId, uint256 batchSize)
+    internal
+    virtual
+    override(ERC721NonceUpgradeable, ERC721PresetMinterPauserAutoIdCustomizedUpgradeable)
+  {
+    super._beforeTokenTransfer(from, to, firstTokenId, batchSize);
+  }
 }
diff --git a/src/upgradeable/ERC721PresetMinterPauserAutoIdCustomizedUpgradeable.sol b/src/upgradeable/ERC721PresetMinterPauserAutoIdCustomizedUpgradeable.sol
index afe0ed3..e400034 100644
--- a/src/upgradeable/ERC721PresetMinterPauserAutoIdCustomizedUpgradeable.sol
+++ b/src/upgradeable/ERC721PresetMinterPauserAutoIdCustomizedUpgradeable.sol
@@ -48,9 +48,16 @@ contract ERC721PresetMinterPauserAutoIdCustomizedUpgradeable is
 
   string private _baseTokenURI;
 
+  /**
+   * @dev This empty reserved space is put in place to allow future versions to add new
+   * variables without shifting down storage in the inheritance chain.
+   */
+  uint256[50] private __gap;
+
   function initialize(string memory name, string memory symbol, string memory baseTokenURI) public virtual initializer {
     __ERC721PresetMinterPauserAutoId_init(name, symbol, baseTokenURI);
   }
+
   /**
    * @dev Grants `DEFAULT_ADMIN_ROLE`, `MINTER_ROLE` and `PAUSER_ROLE` to the
    * account that deploys the contract.
@@ -58,7 +65,6 @@ contract ERC721PresetMinterPauserAutoIdCustomizedUpgradeable is
    * Token URIs will be autogenerated based on `baseURI` and their token IDs.
    * See {ERC721-tokenURI}.
    */
-
   function __ERC721PresetMinterPauserAutoId_init(string memory name, string memory symbol, string memory baseTokenURI)
     internal
     onlyInitializing
@@ -81,10 +87,6 @@ contract ERC721PresetMinterPauserAutoIdCustomizedUpgradeable is
     _setupRole(PAUSER_ROLE, _msgSender());
   }
 
-  function _baseURI() internal view virtual override returns (string memory) {
-    return _baseTokenURI;
-  }
-
   /**
    * @dev Creates a new token for `to`. Its token ID will be automatically
    * assigned (and available on the emitted {IERC721Upgradeable-Transfer} event), and the token
@@ -135,14 +137,6 @@ contract ERC721PresetMinterPauserAutoIdCustomizedUpgradeable is
     _unpause();
   }
 
-  function _beforeTokenTransfer(address from, address to, uint256 firstTokenId, uint256 batchSize)
-    internal
-    virtual
-    override(ERC721Upgradeable, ERC721EnumerableUpgradeable, ERC721PausableUpgradeable)
-  {
-    super._beforeTokenTransfer(from, to, firstTokenId, batchSize);
-  }
-
   /**
    * @dev See {IERC165-supportsInterface}.
    */
@@ -156,6 +150,14 @@ contract ERC721PresetMinterPauserAutoIdCustomizedUpgradeable is
     return super.supportsInterface(interfaceId);
   }
 
+  function _beforeTokenTransfer(address from, address to, uint256 firstTokenId, uint256 batchSize)
+    internal
+    virtual
+    override(ERC721Upgradeable, ERC721EnumerableUpgradeable, ERC721PausableUpgradeable)
+  {
+    super._beforeTokenTransfer(from, to, firstTokenId, batchSize);
+  }
+
   /**
    * @dev Helper function to mint for address `to`.
    *
@@ -171,9 +173,12 @@ contract ERC721PresetMinterPauserAutoIdCustomizedUpgradeable is
   }
 
   /**
-   * @dev This empty reserved space is put in place to allow future versions to add new
-   * variables without shifting down storage in the inheritance chain.
-   * See https://docs.openzeppelin.com/contracts/4.x/upgradeable#storage_gaps
+   * @dev Helper function to mint for address `to`.
+   *
+   * See {ERC721Upgradeable-_mint}.
+   *
    */
-  uint256[48] private __gap;
+  function _baseURI() internal view virtual override returns (string memory) {
+    return _baseTokenURI;
+  }
 }
diff --git a/src/upgradeable/refs/ERC721NonceUpgradeable.sol b/src/upgradeable/refs/ERC721NonceUpgradeable.sol
index 6193a97..d075a01 100644
--- a/src/upgradeable/refs/ERC721NonceUpgradeable.sol
+++ b/src/upgradeable/refs/ERC721NonceUpgradeable.sol
@@ -9,10 +9,10 @@ import "../../../lib/openzeppelin-contracts-upgradeable/contracts/token/ERC721/E
  */
 abstract contract ERC721NonceUpgradeable is ERC721Upgradeable {
   /// @dev Emitted when the token nonce is updated
-  event NonceUpdated(uint256 indexed _tokenId, uint256 indexed _nonce);
+  event NonceUpdated(uint256 indexed tokenId, uint256 indexed nonce);
 
-  /// @dev Mapping from token id => token nonce
-  mapping(uint256 => uint256) public nonces;
+  /// @dev Mapping from token id => token nonce.
+  mapping(uint256 => uint256) private _nonceOf;
 
   /**
    * @dev This empty reserved space is put in place to allow future versions to add new
@@ -20,17 +20,21 @@ abstract contract ERC721NonceUpgradeable is ERC721Upgradeable {
    */
   uint256[50] private ______gap;
 
+  function nonces(uint256 tokenId) public view returns (uint256) {
+    return _nonceOf[tokenId];
+  }
+
   /**
    * @dev Override `ERC721Upgradeable-_beforeTokenTransfer`.
    */
-  function _beforeTokenTransfer(address _from, address _to, uint256 _firstTokenId, uint256 _batchSize)
+  function _beforeTokenTransfer(address from, address to, uint256 firstTokenId, uint256 batchSize)
     internal
     virtual
     override
   {
-    for (uint256 _tokenId = _firstTokenId; _tokenId < _firstTokenId + _batchSize; _tokenId++) {
-      emit NonceUpdated(_tokenId, ++nonces[_tokenId]);
+    for (uint256 tokenId = firstTokenId; tokenId < firstTokenId + batchSize; tokenId++) {
+      emit NonceUpdated(tokenId, ++_nonceOf[tokenId]);
     }
-    super._beforeTokenTransfer(_from, _to, _firstTokenId, _batchSize);
+    super._beforeTokenTransfer(from, to, firstTokenId, batchSize);
   }
 }