Not sure if I'm explaining properly. Let's try again (next step is audio skype :)

Of course, the overflow happens also with 300 years. What I mean is that we don't to which time equals 300 years in an overflow situation. It could e.g. 1971 (in which case we detected this as a wrongly expired registration) or 2021 (in which case we don't detect it as a wrong expired registration, although the problem still happens, as the right expiration value should be 2314).

In the case of PY99 we actually know that it correspond to 1976 in an overflow situation, due to it was investigated when #208 was reported.