In prior versions of the data specifications, M0016 (Branch ID) was an optional field. Even when reported by the HHA, there was no standardized numbering system for branches, so the information was not useful.
CMS is in the process of assigning standardized branch IDs to every existing branch belonging to an HHA or subunit, and this process will be complete by the end of 2003.
Version 1.40 of the data specifications requires that agencies report these standardized branch IDs in M0016 for all assessments with completion dates (M0090) on or after January 1, 2004.
Extracted from OASIS Data Submission Specifications from CMS web site: http://www.cms.hhs.gov/oasis/datasubm.asp#1.40