Why has the number of records changed in my saved dataset?

When I open my saved dataset a month later, the number of records has changed. Why?

A dataset you've saved may contain more or fewer records each month. That's because we reindex all websites in our database each month. You should see the dataset as a set of filters that you save (aka query). So when you click "Save" in the Search Engine, you're actually saving the set of filters you've selected, you aren't saving the number of records (this isn't fixed). When you open the saved query a month later, the results you'll see are based on the most current website indexation. 

Adding the filter "Changes" in your dataset may be of help in some cases.
"Changes" refers to the number of fields in Dataprovider.com that have changed since last month (for example, the website didn't have a shopping cart system the previous month but now the website does have a shopping cart system). You can find detailed information about the nature of the changes using the field 'Changed fields' and our URL Lookup tool.