lastb log is not correct
 

I use the command lastb to check the user login history , however , i found that there are problems , eg .
1. the user has access the system for 3 hours , but the lastb log show the login time is
" Mon Feb 23 09:33 - 09:33 (00:00) " ;

2.the user have login for many times , but the log only show part of the login history ,

could suggest how to fix it ? thx