I dunno ,if dependent origination is a description of reality, then nothing comes from nothing, and that's why nothing is born or dies, because there is no ceasing to exist or coming into existence in reality, it only seems so due to obscured vision.
So, i'd opt for the idea that thoughts arise from previous thoughts, or maybe conditions created by thoughts, which in turn produce new conditions for thoughts arising upon consciousness that sees and forms views oN those thoughts etc..we cannot see all these causal connections clearly in meditation at our level (well, maybe you guys can, I can't!), but I think you can least intuit and infer some of it if you watch closely.
Thoughts being same or different, is again hard to answer since same and different are notions that only exist in a relative sense, Lankavatara says that things are only eternal in their non-eternality, I guess that would mean that technically thoughts are all different from one another?
"Just as a lotus does not grow out of a well-levelled soil but from the mire, in the same way the awakening mind
is not born in the hearts of disciples in whom the moisture of attachment has dried up. It grows instead in the hearts of ordinary sentient beings who possess in full the fetters of bondage." -Se Chilbu Choki Gyaltsen