So if last year I had negative occult blood test but a year later have positive blood occult test, is it possible something was miss last year?

Not necessarily. Some lesion could have developed over the period of a year. Some lesions bleed intermittently and that is why it is recommended that three samples be tested. Blood in the stool in an adult usually warrants a colonoscopy to find the cause of bleeding and to rule out colon cancer. Wish you good health!.