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I just downloaded BG II EE.
When starting the game the version is shown as

In the download folder I have 4 files named as
"patch_baldurs_gate2...." with version numbers: and

When the game is already after installing do I need the first two patch files at all?

Do I need to install all of them in order or only the last one?
I'm new to GOG so I could be wrong, but my understanding of this is that the installer is already the most up to date version. The other patches are available for download in case you had installed the game before the patches came out. So you shouldn't need to install any of them.
The latest patch is already installed. Which basically means you are screwed. The last few patches ruined the game.