I killed 4 deer and a 300lb Bo Hog this past season with Nosler BT's. The four deer were with a 150grn from a 7mm08 and the hog was with a 165grn from a .308. Three deer and the hog were 80-125yds with only one deer running 50yds before piling up and leaving a blood trail Ray Charles could follow, the rest died where they stood. One doe was 322 and dropped like she was pole axed in the head. BT's do the job very well.
I doubt it was the bullet's failure to perform that lead to this, more likely operator error and some buck fever were to blame. The first one could have been a clean miss and the second sounds like a gut shot that plugged up. Did you have access to a dog that you could have tracked her with? 50-60 yds isn't very far to track an animal with no blood trail, she could have started pouring buckets a little further on. If she was running, she had to leave tracks or broken limbs and disturbed brush to follow, though that could be hard to follow in the dark if it was dark.
Hate it that you didn't find the game but you were shooting a good bullet and I have a hard time believing the bullet didn't perform if you hit the vitals.