Sorry about the delay. There are a couple explanations for this...
1. This dog was too old to be bred. The breeding should not have happened and I think that is a leading factor to this dogs struggle/loss of pups.
2. Uterine exhaustion- after the first 4 came, I think that the uterus was already in a tetany type situation where it was failing to move the puppies down correctly and quick enough.
3. One of the last one or two puppies could have died within the last week or so of pregnancy and the death and decomposing affected the other close puppies as well as the uterus.
4. The green could be the material of the placenta unoxygenated...or fecal material...or blood by products.... It is hard to tell with out seeing it. Often when I go in and do c-sections and peel out the puppy and placenta, the attachment is bright green..so what you saw could have been placental fragments.
5. Things that should have happened. Your dog should have had a xray before labor to count the puppies. That would be something you would ask for. It is very hard to tell when a dog is having trouble during delivery. Many times we do count on the owners knowledge and relationship with the dog to help us out. Dogs can take a long time to have puppies...
Many times in our efforts to keep $$ down, we don't intervene when we should with labor. I do think that your dogs primary problem was her age and the possible health of those last 1-2 puppies.
Loss of puppies from failure to thrive or stillborne is not uncommon, but I am sorry that you have had to experience it.
Let me know what I didn't address.