If Lansweeper finds an asset's warranty details today, but not tomorrow, it will indeed keep displaying the warranty information scanned today. The purchase and warranty dates can easily be cleared manually, by hitting the Edit Asset button on the asset page. To remove the actual warranty products though, you'll need to delete the records directly in the database, as you indicated as well.
The following database tables are used to store warranty information: tblWarranty and tblWarrantyDetails. I included a sample script below that deletes the warranty products of computer LAN-010 in domain Lansweeper. You can insert your own values into the script. We do recommend backing up your database prior to running any potentially dangerous statements such as DELETE FROM or TRUNCATE TABLE. Backup instructions are available in
this knowledge base article.
delete from tblwarrantydetails where warrantydetailsId In (Select Top 1000000 tblWarrantyDetails.WarrantyDetailsId
From tblAssets
Inner Join tblWarranty On tblAssets.AssetID = tblWarranty.AssetId
Inner Join tblWarrantyDetails On tblWarranty.WarrantyId =
tblWarrantyDetails.WarrantyId
Where tblAssets.AssetName = 'lan-010' And tblAssets.Domain = 'lansweeper')