Works off the MAC address and computer name I believe and merges the records. So it would retain the legacy data of the old machine, I would imagine, I can't confirm, one for LS Support to answer maybe.
First seen
A computer's first seen date indicates when Lansweeper first tried to scan the machine. The scan may or may not have been successful.
• All computers have a first seen date.
Last seen
A computer's last seen date indicates when Lansweeper last successfully scanned the machine.
• If a computer has never been successfully scanned, it has no last seen date.
Last tried
A computer's last tried date indicates when Lansweeper last tried to scan the machine. The scan may or may not have been successful.
• If a computer's last tried date is the same as its last seen, its last scan was successful.
• If its last tried date is more recent than its last seen, its last scan was unsuccessful.
• A computer's last tried date is only shown on its webpage if its last scan failed.