The Singer and Dabb era covers Season 12 through Season 14 when Andrew Dabb became co-showrunner with Robert Singer following the departure of Jeremy Carver.

If Season 12 was about children coming to terms with their moms as adults, then Season 13 is very much about Sam and Dean as parents.
— Andrew Dabb [1]
What's bigger than God? The answer is nothing. So after we did that, it was really about new directions that we could take our characters that will give them new things to react to? This opens up a lot of storytelling ideas in that way.
— Andrew Dabb on the alternate universe in Season 13 [2]
I think Season 14 is going to be a little less broad in scope and a little more emotional, more personal stories about the guys.
— Robert Singer on Season 14 [3]


Season 12

Sam is captured by Lady Toni Bevell, a rogue operative of the British Men of Letters.

Season 13

Sam and Dean deal with the fall out of Jack's birth, Castiel's death, and Mary being lost in the Apocalypse World.

Season 14

Sam and Castiel deal with Dean becoming Alternate Michael's vessel. Castiel helps a powerless Jack.