"XX" in regards to console commands denotes that the object is from an official plugin (also known as DLC). Usually found in the BaseID or RefID of items or characters, these first two numbers change depending on the order of installation or the order the of ESP files in the data files section of the game launcher.
For instance, installing The Elder Scrolls IV: Knights of the Nine onto a computer with Oblivion sets XX to 01. If The Vile Lair was installed second, XX becomes 02 and so on indefinitely. As another example, if one owns all of the add-ons (as part of the Legendary Edition) for The Elder Scrolls V: Skyrim, items added by The Elder Scrolls V: Dawnguard will, by default, have 02 as their first two digits, while items added by The Elder Scrolls V: Dragonborn will normally have 04.
A way of checking for the XX number for a particular plugin in Skyrim while one is playing is to open the console and either type help along with the name of an item known to be added by the plugin (with the name in quotation marks) or, again with the console open, click on an item in view added by the plugin; the console will then display the full RefID the first two numbers of which will be the XX for that plugin. For example, opening the console and clicking on an Ash Yam or entering the command help "ash yam" will show the XX for the Dragonborn item.
Exception
The Elder Scrolls IV: Shivering Isles is an official expansion pack and not a plug-in, even though it is listed under all the other plug-ins. Therefore, all content has 00 in the BaseID or RefID as the first two numbers, regardless of when it was installed.