Got an answer from Gary Hammonds this morning that may explain what happened.
The birthing of these pups went like this. 6 were born, right off, like in 4 hours. 3 of those six were black brindles.

The other 6 were not born until 12 hours later. As in, #7 wasn't born until 12 hours later.

This is what GH had to say to it:

WERE THE BLACK BRINDLES BORN FIRST ? I COULD SEE THOSE WHO WERE A LITTLE LATE IN COMING PICKING UP A LITTLE TOXIN WHILE STILL IN THE HOLDING PATTERN BUT I AM JUST SPECTULATING. WHEN YOU BREED HER AGAIN AS SOON AS SHE SHOWS SIGNS OF WHELPING GIVE HER A DOSE OF PEN G & PROCANE…..THEN WHEN SHE IS THROUGH A POP SHOT AND PEN DEX CLOR STREP. THE NEXT DAY USE PENN AGAIN AND POP. ANY WAY IN THE FUTURE JUST PRAY FOR BLACK BRINDLES AND KNOW THAT IT WILL HAPPEN. THE BOTTOM LINE IS THAT YOU CAN’T QUIT AND LEARN FROM EVERY EXPERIENCE. MAY THE GOOD LORD BLESS YOU IN ALL YOUR DOGGIN AND OTHER STUFF TOO !