Hello Michael,
Brady here with the Blue Button API Team. Currently the BB2 API only has one effective date for all Medicare Plan Segments. This means that the effective date, mapped in coverage.period.start, for Part A & Part B will be the same. The Blue Button Team is in the process of working with our upstream partner, who provides the data for the BB2 API, to get the distinct effective and term dates for all the Medicare Plan Segments that are available. We hope to have the different segment dates mapped in the future.
Please let me know if you have any further questions.
Thank you!
Brady Fausett - Blue Button API FHIR Specialist