I don't think that quite works out right. Praxis' explosion happened fifty years befoe the Enterprise C battled the Romulans.
As to the technicalities of the timelines in the OP, I would suggest that the Tasha timeline is the alternate one. It completely deviated from the one we had been watching for the previous two and a half seasons. The only way the alternate timeline exists is when the Enterprise C emerges from the rift, and it ceases to exist when it goes back. The actual timeline is therefore always the corrected one.