Generally if there is a big time gap between deliveries (like there was today) then a pup is stuck and will be stillborn. Or Momma is too tired to keep pushing like she should. Sometimes it also backs up the rest of the pups behind it and you lose all of them.
The biggest problem with large litters is the Momma getting tired of birthing and you have to make sure you get them all out of their sacks if she is too tired to do it, or she'll not get to them in time and they suffocate. Like today, Joy took over 12 hours from first pup to last and though she did clean the sack, she just left the pup lay rather than give it more cleaning time like she should have. She was wore out.
As for live pups, sometimes a new mother will lay on one by accident, which kills it and that's really sad. Other than that, I just make sure each one is getting its fair share of momma's milk. Generally if you get them through the first 2 weeks, all is good. I start puppy food at 3 weeks of age to help Momma out.