
Samsung Galaxy Wide
Every official firmware build for SM-G600S, newest first: one row per build with all regions (CSC) that received it.
Each firmware build has its own page at https://samfirm.shop/build/{PDA}, where {PDA} is the build number from the list above. Example: https://samfirm.shop/build/G600SKSS1BTJ1
Specifications of SM-G600F, a regional variant of the same device. Chipset and SIM lines are left out: they can differ by region.

SM-G600F

SM-G611S

SM-G610S

SM-G615FU

SM-G6200
You can find the firmware on the model: SM-G600S page.
Yes, all firmware files for SM-G600S are 100% official, original, and obtained directly from Samsung servers.
To flash SM-G600S, you need to download the appropriate firmware, put your device into Download Mode, and use the Odin tool to load the BL, AP, CP, and CSC files.
Downgrading is only possible if the bootloader version (binary bit) of the old firmware matches the current one. Always check the binary version before flashing SM-G600S.