Hi Mark,
Assets scanned via SNMP are usually uniquely identified with their MAC address. Because most of the devices are being merged, this would indicated that they all share a generic MAC address.
If you can find the generic MAC address used by the devices, you can run the database script below to add the MAC address to the blacklist. This will prevent the MAC address from being used as a unique identifier.
INSERT INTO tsysMacBlacklist (Mac, Comment) VALUES ('00:00:00:00:00:00', 'your blacklist comment')
GO
UPDATE tsysupdate SET MacBlacklist = GETDATE()
As for the assets without a MAC address, they will be uniquely identified in another way, how Lansweeper handles identification can be found here: https://www.lansweeper.com/kb/149/how-lansweeper-uniquely-identifies-assets.html