Then it seems like those select members might have a stale address book.
On the affected users not seeing the updates try this:
For the Lync 2010 client:
STEP 1
Execute the following command in CMD prompt - running with an administrator account for the PC, or right-click Run As Administrator if you have User Account Control enabled:
reg add HKLM\Software\Policies\Microsoft\Communicator /v GalDownloadInitialDelay /t REG_DWORD /d 0 /f
STEP 2
Go to location where the Lync profile is in C drive of the PC:
Ask the user to exit (not just sign out) Lync , then to delete the folders from that location, and then to re-login in Lync again. Path in 2010 C:\Users\User\AppData\Local\Microsoft\Communicator
In this way the SIP profile is recreated and the connection to Address Book rebuild.
For the Lync 2013 client:
STEP 1
Execute the following command in CMD prompt - running with an administrator account for the PC, or right-click Run As Administrator if you have User Account Control enabled:
reg add HKLM\Software\Policies\Microsoft\Office\15.0\Lync /v GalDownloadInitialDelay /t REG_DWORD /d 0 /f
STEP 2
Exit Lync and clear the client cache.
Delete the folder sip_username@domain.com from %userprofile%\appdata\Local\Microsoft\Office\15.0\Lync .
Check inside the sip_username@domain.com that that the two files (GalContacts.db and GalContacts.db.idx) are created (takes about 15 seconds).
Let me know if it works.