It also occurs to me that at some point the Romulans discovered they had a future-history Tasha Yar in their possession and would have interrogated her for all she knew in terms of history (though clearly it had changed, certainly she would have some valuable insights) and technology...thereby giving the Romulans of 2344 somewhat of an advantage over the Federation and the Klingons of that time.
I've made this assumption; it's how I make some things in Nemesis
make sense in my head. Why did the Romulans clone Picard? When he was in command of the Stargazer
they couldn't have known that he would be important someday. So, either the Romulans knew something about the future -- or they had a cloning program that covered hundreds of Starfleet officers. The assumption I make, then, is that alt-Yar revealed some things about the future that eventually filtered into the cloning program.