Yes, it could be blocked with either debris or blood, in which case ti would cease to function and would be rendered useless.
How do you know if it is blocked? Well apart from getting a Dr to look with his auriscope, a simple method would be to nip your nose, press your lips together and gently at first, blow down your nose. If you can hear or feel air coming through your ear, or a noise, then the grommet is patent, but if not then it is blocked and there is nothing that you can do to unblock it and it will need replacing.