Does Google know where it is or where it went?

Probably a noob question.

[mgpapas]

About six months ago I redid alot of my site and probably stupidly rather than making a redirect page or have people end up with a 401 if a link went to that page I set it up so that all requests for non-existant pages go to the home page.

So come september and BANG I'm totally knocked out of the rankings. I assume it's because Google thought all those links it followed from other sites went to the page indicated and that it was a duplicate of the home page.

Am I correct or does google look at where it is and say "this isn't that page"

I know yahoo doesn't because when doing a backlink check I found urls like mysite.com/widgets/widgets.html when I've never had a page called widgets or a directory called widgets but apparently for some reason or other someone put that link on their page and yahoo thought it was there and cached my home page as that page.

[oddsod]

If you run those URLs which redirect to your homepage via a server header check - and if they come up with a 200 - then it's probably safe to assume Google sees the pages as dupes.