Look at Skyrim - Patch.bsa .
In Elder Scrolls lore, the concept of Dragon Breaks —moments where time splits and multiple timelines exist simultaneously—is well-established. The Patch BSA is a Dragon Break in file format. skyrim - patch.bsa
Skyrim - Patch.bsa is the smallest of the core BSAs. It’s also the most dangerous. When Skyrim launched on 11/11/11, there was no Patch.bsa . The game’s core data lived in the original Skyrim - Meshes.bsa and its siblings. Then came Update 1.2, 1.3, and eventually 1.9 (the legendary “Legendary Edition” patch). Bethesda has a workflow: when they fix a bug, they don’t go back and rebuild the original 8GB BSAs. Instead, they create a new BSA that contains only the changed files . Look at Skyrim - Patch