If very few dinosaurs left evidence for their existence, how do we know they existed

The ones that didn't leave evidence. How are we sure that they existed without evidence?

As for the ones that didn't leave evidence, we aren't sure. We can only make conjecture that they most likely did, based on the fact that they need breeding populations in order to survive

We aren't in the habit of presuming that the ones which didn't leave evidence existed. We catalogue new species as evidence for them is found.

Suffice to say, there are plenty of species for which we have found evidence, and we can be reasonably certain that at any given point, we haven't found them all.

Our technology allows us to recreate what an animal looks like.