I've been perusing BrickLink for a while, and I noticed that essentially all sets are listed with a "-1" after the LEGO set number. For example, Set 41164, Enchanted Treehouse is listed on BrickLink as 41164-1.

What's the purpose of the "-1", and more specifically, what would a "-2" or even "-3" set number represent?

• Does it represent a version number (e.g. a revised or post-recall version of the set would be numbered 41164-2)?
• Is this a country code?
• Is it just a site-specific affectation?
• Is it currently unused, but reserved for future use?