I will move this to adventure games discussion forum since this is not for a game help.
Why don't you write the walkthrough writer and see what she-he says. Thanks and glad you got through the game.
Just some comments:
Most walkthrough writers write what they experience in playing the game - some just barebones; some step by step. There will be differences in 2 wts of the same game since the logic of each gamer is different from the other. So sometimes there will be things not written because it is 'presumed' that it is obvious or that was not how that writer played the game. Sometimes, they omit things and leave it to the imagination of the gamer or not remove the thrill of solving the puzzle for the gamer.
As for additional maps, pictures, updates, etc... - sometimes it is also skipped because it is presumed that it is in the descriptions, the amount of time involved, lack of technology or expertise, etc...
Most walkthroughs are written to help on difficult puzzles or give a boost to gamers to start-play-continue the game. They are not meant to play the game for the gamers. There will always be some missed parts, typos or glitches.
I, like you am personally grateful for the time given by the walkthrough writers in doing them since I know how difficult it is to cover all aspects of the gameplay, the time involved and the type of comments received when gamers missed a part or misread the walkthroughs or not clear in descriptions. We appreciate the comments about being of help to others as you have done. Maybe that is why some walkthroughs writers still continue to write, although they are becoming less and less.