: The first release was missing files, levels, or cinematic sequences.

: The original group broke specific community "Scene Rules" regarding file naming, compression, or tagging.

When a group releases a file like Tiny.Troopers.zip , another group might mark their version as a "PROPER" post if the original release had a specific flaw, such as:

: The security bypass (crack) doesn't work on all operating systems or hardware.

: The game crashes at a certain point or has broken audio/visuals.

Essentially, a "PROPER" tag is a claim that this specific upload is the that should be used instead of the earlier "nuked" (invalidated) version.