Different LastAccessTimestamp for index with 2 columns !!

Database

Different LastAccessTimestamp for index with 2 columns !!

Hello,

 

i'm trying to track secondary indexes which are not use , but I don't understand 2 cases below : 

- Can anyone explain how it's possible to have in dbc.IndicesV view, 2 different LastAccessTimestamp for 2 columns of the same index ?

- How does it mean when I have a null value for accesscount with lastaccesstimestamp not null (about one year ago) ?

 

TIA