Annemarie, speaking as someone who has had 3 biopsies I can try to tell you how it was explained to me. Sarcoidosis is a granulomatous disease. As you probably already know Granulomas are a bunch of cells that gang up and bind to create an area of inflammation, too much of this will render an organ useless. There are other granulomatous diseases as well such as tuberculosis, Histoplasmosis or Syphilis. When a tissue sample is taken for example from a spleen like in my case or maybe a lymph node it is then examined by a pathologist who looks inside the actual granuloma. If it were TB the granuloma inside would contain a necrosis and multinucleated giant cells or (Langhans giant cell) might be present as well, so they look at this and say well this is consistent with TB! and you have got a diagnosis. Well with sarcoids they kind of look into the granuloma and find nothing. Nothing that's right, nothing. In reality biopsy or not there is no test that can confirm 100% that you have sarc. Doctors diagnose you when everything fits and you are negative for everything else.
I had my first biopsy when they removed my spleen (rendered useless by sarc). That's when I got diagnosed.
Second biopsy last year when I had a huge mass above belly button. It ended up being a crazy huge lymph node. and the last one just a couple months ago on the lymph nodes on my face under my ear.
Hope this helps and good luck