cached pages & update backlinks

[helenp]

Do we know anything about how often backlinks and cached pages are being updated?

Itīs so strange, one of my backlinks is an redirection to another company and the cached page has an hidden link to my and several other related sites.
Seems to be old, though in page says copyright 2003.

If I type that companys url, the cached page shown is completely diferent, and no hidden text, seems to even changed owner of domain. and copyright 2004 is stated.

How can one page has 2 diferent cached pages?