Question re the progression of Stage 4 NSCLC

Hi All- I have a question for all you seasoned hospice nurses. My 79 year old father was diagnosed with Stage 4 undifferentiated NSCLC on November 12 , 2008. He has a 7 cm tumor in his rt middle lobe and a 2 cm in his left upper. At thet time he was 123 lbs...usually 145. He opted for no treatment and was given 4-6 months prob. less. He was placed on Hospice. Hospice has been wonderful. His nurse comes every week and they basically look at each other. My dad has gained all his weight back and seems totally normal to me. His nurse says the only sign of cancer is no breath sounds in the rt middle lobe. Nothing else has changed since diagnosis. He is on no meds or oxygen. He has no pain. He says he feels tired when he works in the yard etc but rests a few min and is back at it. I came home the other day and he was sawing down branches with a hand saw.
My question to you all is, does this seem odd. I guess I would have expected some symptoms by now. Even his nurse is stumped.
What do you all think?
Thanks so much.