Sorry about all your birds dying. It seems pretty common to see a variety of symptoms, especially as they get older. I think it has to do with where in the body the virus attacks first. Maybe caused by different strains.I've had 5 (my whole flock) die from Marek's and they all died somewhat differently, but none of them had that much energy. It usually started on one leg, where there was a limp, not both all wobbly like that. They often had swollen bellies and many of the other hallmarks (puffy eyes, white patches on eyes).