A very very old Clue board game?

I have this extremely old Clue board game from my step dad. His other kids are a lot older than me and they used to play this exact board game all the time. I found it in the garage tapped closed. He told me he tapped it shut because his was moving and didn't want the pieces to fall out. It has been tapped shut for 10 years. I opened it, probably two years ago, to play with my friends. It is not an original but I could guess it was not only very close but maybe even the second version of this American version of Cluedo. I has a Lounge, Hall, Study, Dining Room, Kitchen, Ball Room, Conservatory, Billiard Room, and Library. It is just the normal Clue, no extra rooms, people, or weapons. I was looking at it today and was trying to find an answer. It has four Secret Pages. It has two Secret Page cards and four Treasure cards. I read and read the instructions but never found any information about the cards, just the Secret Pages on the board. I don't get it! I thought the cards are in the wrong game box but it says Clue many times on the back. Hmm... Do you guys know anything about the cards or the version? I would love to know! I spent awhile looking up information and pictures but I couldn't find it anywhere. The cover has Mrs. Pea sitting in a chair, Miss Scarlet smoking and kind of lying in a chair, Prof. Plum reading a book and smoking a pipe, Mrs. White hiding behind the curtain, looking VERY guilty, Col. Mustard looking at something on the fireplace, and Mr. Green sitting in a chair with a cigar looking very surprised. The box cover is pretty faded and has a white stripe on the top of the picture saying Clue. So back to my question, do you know the version and what the cards of the Treasure and the Secret Pages are for? Thanks!