Can post traumatic stress disorder symptoms show up many years after the event that caused them?

PTSD late appearance. Yes! and many years after discharge from military. Can result from accumulated stresses successively in life, or not even accumulated stress besides the war experience [or any trauma, example = surviving severe life threatening sickness and severe long duration in ICU with lasting severe pain and emotional duress].
Delayed PTSD. Expose the person to the right trigger and the old pain & memories can come cascading back.