According to Limited Run Games tweet , their version contains additional content including "Requiem for Innocence" (prequel chapter) and "Reincarnation" (sequel chapter).

Does anyone know if the GOG version has these additional chapters? If not, are there plans for them to be released here soon?

No, and no idea.

The console version is a remaster including all content. Higher resolution stuff etc. PC only has inferior versions of the game and the prequel. The Sequel chapter is not on PC as far as I know.

The Prequel chapter is currently exclusive to Steam, I wish I knew why.

'A Requiem for Innocence' is also available at MangaGamer's own shop but it oddly shows up only if you go access their adult section and search from there.
Unfortunately they still have problems with their payment processor so CC-payment is not available (it's been off from the end of June). They do give alternative ways to buy by asking them.