What if my older infant still has an unusual head shape?

Get an x-ray. If the head shape has not normalized by 3 months of age, skull x-rays should be taken to be certain that all of the separations ("sutures") between the skull bones are open. If they are open, the baby might be referred for evaluation for a skull molding helmet. If there is a question about the bones of the skull, a ct scan may be ordered to clarify the situation.
So what. Abnormal shape only implies malfunction, but does not guarantee it. The internal anatomy of the skull and lack of compression on the brain tissue is the most functionally relevant problem to assure normal function.