Finding the no of not logged in since X months or never in SAP BOBJ BO System and what is named Vs Concurrent

What is concurrent users licenses ?

Concurrent user licenses are nothing but at a point of time number of users allowed for a system to access , ex: 50 concurrent user Licenses means , 50 users can login all at once , still system allow to login until 50 licenses reached or users logged at that point. 

Note: with the above , provided your SAP BO system has proper memory assigned in the configuration or settings of the BOBJ Settings 

Whare are named user Licenses ?

NAmed users are more indipendent of the Concurrent sessions, like you can N Number of sessions logged in if you have N Named User Licenses 

Users who have not logged in for the past 6 months:

SELECT TOP 5000 SI_NAME, SI_LASTLOGONTIME FROM CI_SYSTEMOBJECTS

WHERE SI_NAME NOT IN ('ADMINISTRATOR','GUEST') AND SI_KIND='USER'

AND SI_LASTLOGONTIME < '2016.09.03' ORDER BY SI_NAME

Users who never logged in to system:

SELECT TOP 5000 SI_NAME, SI_LASTLOGONTIME FROM CI_SYSTEMOBJECTS

WHERE SI_NAME NOT IN ('ADMINISTRATOR','GUEST') AND SI_KIND='USER'

AND SI_LASTLOGONTIME IS NULL ORDER BY SI_NAME