Timing Light Accuracy

Do inductive timing lights ever go bad and give off inaccurate flashes? I've got a vintage Craftsman chrome inductive light that I'm questioning because of how much initial timing my 340 wants. I've verified the TDC mark - it's spot on. Maybe this 340 just an anomaly because it seems to want 30* initial adv.

Without having a second timing light to check it against, I'm curious if these thing ever go bad.

images?q=tbn:ANd9GcQKezUYSrl66b90mVhMUeMmdRlkvWqEMKYKXd7ylj82a_PPKMrSQw.jpg