UBB.threads PHP Forum Software Community Forums UBB.classic UBB.classic 6 Support Member Management question

I'm trying to create a list by searching
members who have been have been active since a soecific date. I have 4215 members but I don't seem to get a higher active amount than 2283 nomatter wich date I search. I can see that some members miss their Last active note
example
Last Active: --
Last Post: --
Last IP: --
Reg IP: 209.197.129.19
Reg Date: December 11, 2005


Can you please explain what creats a last active log? Have 2283 members registred and revisited but the others who registred never returned???

Member Management
Date Options
Last Activity Date:

Thanks