Ordinary cells can be accessed from as many locations as configured, generally; system, site and project.
DataGroup Annotation Cells are different, they can only be accessed from one file. This file name and location is defined by BB_ANNOTATION_CELLLIB.
The default location is in C:\ProgramData\Bentley\AECOsimBuildingDesigner V8i Ss6\WorkSpace\BuildingDatasets\Dataset_<region>\cell\Annotation_DG.cel.
If you intend to make modifications or add to the delivered cells we recommend that you do so in a site or project level copy of the delivered Annotation_DG.cel.
If you have company dataset folders, setting BB_ANNOTATION_CELLLIB = $(COMP_DATASET)cell/Annotation_DG.cel at the site level directs all users to that file, which should be write access to admin users only (to maintain standards) so does not allow project specific annotation cells. Copy the delivered library to this location then amend as required.
Setting BB_ANNOTATION_CELLLIB = $(PROJ_DATASET)cell/Project_Annotation_DG.cel in the PCF overrides this but relies upon any updates to the company standards being imported to the project. This can be done using the normal import model process. Copy and rename the delivered library to this location.
Just to reiterate, it is not possible to pre-pend (or append) multiple DataGroup Annotation Cell libraries, e.g.: BB_ANNOTATION_CELLLIB < $(PROJ_DATASET)cell/Project_Annotation_DG.cel will fail with the message center error:
"BB_ANNOTATION_CELLLIB points to an invalid file"