Not quite sure I follow you, but it's possible we see the same issue: My Google calendar is visible on my Android phone using the Google Calendar client, on my Thunderbird Calendar with Provider and through any web browser at
calendar.google.com. I have read access to another calendar that doesn't belong to me. It shows up quite nicely when I view my calendar through a web browser and in Thunderbird/Provider. The shared calendar does not show up on my Google Calendar client on my phone.
Nothing to do with Provider though. Seems to be a deficiency with the android Google Calendar.