The number of people who've interacted with the Bronze Dragonflight is relatively small, all in all - they keep themselves pretty isolated and their contingent of mortal supporters is also quite small, respectively. I also doubt even the Timewalkers are made aware of the full nature and scope of the timeline, down to its minutiae. Even Nozdormu himself seems unaware of that, given how often he's expressed surprise, confusion, or consternation at any number of occurrences. He knows a lot more than your regular Joe for certain, but not the entirety of it.