There is a diffrence between Duplicate and Replaced.
Duplicate- The orignal book is lost/misplaced & no one knows where is the original book, and FIR is launched, given the news in news paper, gone through a long procedure and issue a duplicate book from Excise. with DUPLICATE is written on the book. car value will depreciate. orignal book which is lost can be use with some other vehicle with chassis tempered or what so ever.
Replaced- Original book is damaged, some kid drop some tea or ice-cream on it or it fell into the water or some one washed the pant while book is in pocket and it is now un readable, so gone through a small process, submitted the original book in excise department and issue a replaced book, whereas the officials put the original book in the file and any one can go and see the file and verify the book as well. (there is a procedure to check the file off course)
no need to worry about the replaced book but do check the original file and check your self the original book in the file and the application for the replaced book is present in the file. Car value will depreciate but not as much as having duplicate book.
just my 2 cents. I might missed something so wait for an expert to respond in detail