Complex thyroid nodule biopsied said to be benign... now regardless of the diagnosis... could it be possible that nodule is cancerous and biopsy missed it?

Yes: I assume you are talking about a needle biopsy. The larger the nodule, the greater the chance of sampling error. For small nodules (1-2.5 cm) sampling error is low. With nodules approaching 4 cm in diameter the sampling error becomes unacceptable. Those nodules need to be removed, usually as part of a thyroid lobectomy (removing half the gland) or a total thyroidectomy.

Possibly: Thyroid nodules are notoriously difficult to interpret biopsy results, because the nodules themselves are often "complex" meaning non-uniform, and thus one portion may look benign while the other malignant, .