How much can be wrong define a golden age of an artist?

[mat.bez.lima]

Frequently the singers or bands have a so-called golden period when at least almost all albums released in that time are considered at least excellent, if not masterpiece. But how much define a golden period for an artist can be valid? Did you have sometimes considered this a little simplist and superficial when really analising the whole career of someone? Did you also find really great albums of an artist that, in your opinions, are underrated, forgotten and criticized just because aren't from the "golden period", but listening to it you can't see another reasons, beyond just the fact that it is not an album of the golden period, of so much criticism?