I suspect the quality of the DNA available is pretty bad. It's probably fragmented, with bits missing and thus useful only for comparing gene sequences to those of other animals to see how closely related they are (which has been done), rather than for cloning which at this point requires intact choromosomes so far as I'm aware.
In Thursday's world, they've obviously figured out a way to patch the missing parts of the sequence with DNA from other birds (preferably dove, but apparently flamingo works too, with odd results). And they apparently still had glitches, such as a lack of wings in pre 1.7 models, and oddities in the sleep cycle (according to Thursday), and some rather strange looking dodos in the vet's office illustration that didn't make it into TEA:
[
www.jasperfforde.com]
To quote that page:
Firstly and central to the picture is Pickwick himself, looking like every other pet that one might have taken to vet to have a jab or something. He has no wings because he's a Version 1.2 and they didn't get the sequence complete until V 1.7. The dodos queuing up with their owners in front of a desk clerk named Crick(1) are all different shapes and sizes (2) indicating that gene splicing is not an exact art and all the owners are talking about the different versions - the same way car enthusiasts might compare engine sizes.
(1) Crick and Watson and Wilkins and Franklin discovered the nature and importance of DNA in the fifties. I think Mycroft probably had a hand in it, too.
(2) One has a peacock's tail. Another has three legs.