This is a little SQL web report I created that identifies systems which have not reported hardware or software inventories within the last 14 days.

SELECT DISTINCT
    SYS.Netbios_Name0,
    HWSCAN.LastHWScan,
    SWSCAN.LastScanDate
FROM v_R_System SYS
…

Full LessThan14Days SQL Code Here

Note: you’ll want to change the collection ID to be the one you need.  Or modify the code to prompt for a collection would probably be even better still!