Update specific field

Hi David,

To start with I use google webmaster tools, and each time there is a new feed import, a sitemap is created and sent to Google.

Here is my issue. I'm dealing with books feeds. So far I create a new product database, import, normalize due to specific issues, then
substitute the old database by the new one. The disruption of service is only of a couple of seconds.

However between feeds we can have hundreds of products that disappear and my old friend Google does not like that.
It keeps sending emails saying that I have 404 pages. Google seems annoy (which is true because products do not exist anymore)

So here is my idea in order to solve this issue and keep Google calm.

Duplicate products database (products_import)
Add 2 new fields (import_ref, date import)
Import feed in duplicated database
If dupe_hash exist update price else import product
Mark imported/updated product with a reference (new import, updated) in import_ref field and add date in date field
Run database and select all products with no reference (import_ref), update price to 0 or N/A, update buy_url to empty and update import_ref with (N/A ref) and add date.

Doing so would solve the 404 issue. Moreover this would leave the option to extract old products by dates at some point and send an update to Google.

I know that updating a database can become a mess if not done properly. However, have you thought of a better way to deal with this issue? Is there a flaw in my reasoning?

regards,
john