Over the years, park buses from BC have been shared with some or all of the Epcot resorts. It has varied over the years and it varies from park to park. Generally, however, while the bus service from BC is pretty good, one problematic area has been the bus to MK in the morning. Generally, those buses stop at YC first, then BC. I have seen it happen that the bus fills up at YC, so that no one (or very few people) at BC can then get on. This can lead to waits..