Are thrombocytes the only formed element in blood not synithesized in red bone marrow?

No, thrombocytes (platelets) are not the only formed elements in blood not synthesized in red bone marrow. While most blood cells, including red blood cells and most white blood cells, are produced in the red bone marrow, platelets are actually fragments derived from megakaryocytes, which are also produced in the bone marrow. However, lymphocytes, a type of white blood cell, can mature in lymphoid organs like the thymus and lymph nodes after being produced in the bone marrow.