So they had a corresponding mosquito for every single dino species?

Maybe not every dinosaur, but you make a good point.

That's the way I've always understood it to be the case.

Why do you think this is a plot hole? Leaving aside the unlikelihood that you could find any usable DNA in mosquitoes frozen in amber; insects caught in amber are not uncommon. How many species did we actually see? Maybe a dozen? two? Out of the thousands of species which likely existed, or even that we have found fossils for?

Given the basis of the premise, this is hardly a stretch of logic or probability.

Yes, that seems to be the case (the novel also mentions gnats and ticks preserved in amber). How is this a plot hole? Was there something established in the plot that contradicts this?

The blood of several stored in its body that was later separated by the scientist for its dna inside.

They probably went through thousands of mosquitos. Not every one produced viable dino-DNA.

Something the film doesn't go into enough is the fact that they gathered multiple dinosaur DNA captured in amber in various mines around the world. Hammond and Ingen Corporation was obsessed with amber mines in the 70's and 80's leading up to Henry Wu's first extraction of Dino-DNA, deployment and study on Isla Sorna, and then transferred to the park at Isla Nublar.