Why does BrickLink append a -1 to so many set numbers? I've been perusing BrickLink for a while, and I noticed that essentially all sets are listed with a &quot;-1&quot; after the LEGO set number. For example, Set 41164, Enchanted Treehouse is listed on BrickLink as 41164-1.
What's the purpose of the &quot;-1&quot;, and more specifically, what would a &quot;-2&quot; or even &quot;-3&quot; 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?
TLG hasn't always been particularly careful about their set numbering, so the community has taken to adding -1 to the end of the set number to handle cases where there may be duplicate set numbers used by TLG. For example, here's what we refer to as 8858-1:

And 8858-2:

As others have pointed out, this also helps to track minor adjustments to sets (re-releases, box differences, inventory adjustments, etc). Bricklink maintains a list of sets that are similar and have the same official set number but which are assigned unique suffixes for various reasons.