Update of client by SEPM

Hi all,

In my enviroment there is the following scenario:

1. The SEP clients receives updates directly from SEPM server;
2. The SEPM server receives the updates from an internel LiveUpdate server and from Symantec LiveUpdate server.

I don't understand why the clients have different date of signature definitions and why their signature date is different from the siganture date of the SEPM server.
In a normal use case the date SEPM signature should be equal to the date of clients definitions, true?

Thanks