Yes we can be sure because science works by others being able to repeat tests conclusively or it wouldn't be science. What the heck do you think scientists do just make stuff up, lol?But no one can be completely sure of what the scientists and others have on display as dinosaur bones. No one can be sure if they are real or not and the fact that these fossils are magically discovered in the last century seems to make me more skeptical about the dinosaur drama...Seriously no one discovered these fossils till 19th century? Lol, gotta admit, a joke right ? ..I am not a believer of dinosaurs/dragons.
Another strawman with "magically" discovered. No magic, you dig in the ground and find bones. Around our area people recently found a mammoth quite by accident. As others have mentioned bones have been found for much longer than you prefer.
There is objective evidence for dinosaurs that other fields of sciences, other than fossil science, are able to verify. Suit yourself.