Did you have any luck with this?
I too am having similar problems. I have just created a new feature linked annotation feature class for an existing point feature class containing 2500 features. When I create a new feature I also get a new annotation feature, as expected, however I cannot see any way to successfully create the annotations for all of the existing point features. I can obviously convert the labels to annotations and append to the new annotation class, however it does not seem to respect the classes I have set up for the annotations; it creates new default ones.
The only other way I can think of doing it would be to copy the 2500 features across into a new feature class, thereby 'creating' the new features. Unless there is a GP tool I have missed?