Maybe book explains it better but I haven't read it.
Their only dino DNA source was blood from the stomachs of mosquitoes found in amber that fossilized when dinosaurs still lived, correct?
Let's suppose that it is possible to use that DNA as a foundation and "fill in the blanks" using modern frog DNA.
But how did they know whose DNA it was to begin with? Was it t-rex, velociraptor or vegesaurus? All they had was "some DNA" with nothing to compare it to. If they didn't know who that was - how could they possibly aim for something specific while filling in the blanks?
Or was it more like "well, let's splice some frog DNA in missing spots, put it all in chicken egg and see what develops" approach?