I'm watching this series (ST), after a regular vision of TOS and TNG, in a nonlinear way. I have already watched also Enterprise, but I'm still at S5 of DS9, and I've missed Voyager at all.
Now I'm watching Discovery (a little critic on this series may be the absurd Klingons' morphology, the exaggerated move away from original TOS' layout (okay, I understand its allocated budget was a grain as well as the effects possibilities, but in this way you have too much of a good thing! 🙂), the incredible spore drive, but complexly I like this series very much, preserving in my opinion the spirit and style of ST with a great screenplay and direction).
After the emotional aside 🙂, the question:
Ref. Chakoteya, S1 E10, XVIII scene [Ready room]:
BURNHAM: There may be some kind of temporal anomaly at play. It's unclear, but data suggests that in the future, the Defiant will encounter a phenomenon that'll bring it into this alternative universe's past.
I have thought and rethought about this assertion and my current memories about Defiant (as said, I'm fixed at DS9 S5 E21, Soldiers of The Empire, and in addition I honestly cannot figure out what does that have to do with the Discovery's Defiant), but I cannot hit the bull's-eye, solving my doubts.
I know the DS9 crew has traveled two times (basing on my current S5 E21 state of knowledge) into the Mirror universe, but I don't see when the Defiant fell into the timeline of Discovery.
So, what are they referring to with the future Defiant, and in which season and episode does this happens?