To be clear, the annotation needs to be inside a subsystem block in the library. Then after you updated the annotation in the library, it should be automatically reflected in the model where the subsystem block is used. If not immediately, then do Ctrl+D (update) the model.
If the annotation is in the library but not inside the subsystem block (e.g. an annotation in the root level of the library), then it will not be dragged to the model when any of the library block is used, even when the annotation is "linked" to a block in the library.
In other word, if the annotation appeared in the library does not appear in the model when a library block is dragged to the model, then later, after you update the annotation in the library, they will not impact the model.