Version 1.6.640 is significant because it was the "Anniversary Edition" update (released November 2021) that introduced the Bethesda Creation Club menu and broke compatibility with the previous Script Extender (SKSE) and many mods. A "verified" tag in the modding community usually refers to a or a specific Mod Organizer 2 (MO2) Instance that is confirmed to be stable for that specific game version.
Every owner of Skyrim Special Edition on version 1.6.640 has access to four core "Verified" (Creation Club) items for free: skyrim special edition 16640 verified