This info is lost in the new ocs RC 2.6 version because was replaced by the new dashboard page:
Machines in DB xxxx
Machines Inventoried xxxx
Machines contacted today xxx
Machines Inventoried today xxx
Machines not seen in more than 30 day(s) xxx
Number of SNMP devices xxx
Number of non inventoried network interfaces xxxxxx
I wonder if it's possible to include a query of machines not seen in more than 30 days in assets category. It seems not because selecting computer -> last inventory, only specific (not relative) dates are allowed. I mean, you can use: last inventory more than 28 nov/2018 but not last inventory more than NOW() - INTERVAL 30 DAY.