One wrinkle with this whole Manage My Health thing is how they retain data for customers they no longer have. I know this because my local practice switched from Manage My Health to MyIndici, but our Manage My Health accounts were kept open, with no indication the accounts would ever be closed or data deleted.
I complained to my local practice earlier in the year, and eventually got the answer that Manage My Health were the ones who made the call to retain the data.