Are 2 colonscopies in 2 years sufficient to rule out any flat polyps, cancers,etc? both colonoscopies were performed by experienced endoscopists.

Yes: If both colonoscopies negative, I would feel a high degree of confidence that you do not have a polyp. This is a thought if you are particularly worried about colon cancer talk to your doctor about Cologuard. This may be a better screening test for you and safer than colonoscopy. However, this test is primarily used for screening in people 50 or older at this time.