Good question, and I hope that someone can share some technical knowledge about these delays. I assume that the labs are following very strict testing protocol that can withstand scrutiny when the inevitable appeals are launched. If you remember the OJ Simpson trial (a gong show theatre, but it revolutionized how lawyers attack DNA results) the defence will not be to attack the science, but to attack the testing procedures and the people handling the products. Stricter protocol and perhaps a lack of qualified human resources may be the reasons for these delays.
Really good question - I am sure there are good reasons but it doesn't help that it takes so long to notify riders, federations and organising bodies - I can cope with us joe public having a longer delay. Due process seems to take a while - be good to know why?