Are you using the freeware version or the trial version? When Lansweeper is first installed, a 20-day trial is initiated. Afterwards, the software reverts to freeware.
When Lansweeper rescans a computer's software, software information is updated and you'll see any software changes reflected in the scan results.
The freeware version of Lansweeper only supports scanning with LsClient. The LsClient scanning method respects item wait times. So depending on what the "SOFTWARE" wait time is in the configuration console under Scanning Options\Item Wait Time, it may take several days for software information to get updated.
Premium versions of Lansweeper contain "Full Rescan" options, which allow you to rescan all computer information at once.