You’re getting awfully close to sounding like the psychos who say that all fossils are invented or placed on earth by the devil to confuse humanity about the age of the earth.

Most mounted dinosaur skeletons contain real fossils. Many museums have diagrams showing which are real and which are recreations of fossils that were missing or too damaged to mount for each specimen.

Paleontologists can determine what the missing fossils looked like based on other specimens and looking at what they have in context of other similar species that have more complete skeletons.