Network problems and efs qcn sec

Hi i have few phones with netowrk problems. This is s5, note 2, s3 and s4.

I i have fe questions:

1. If i put *#0011# i seen imei pass – does it mean ef qcn sec and cert is ok, or schud i search problem?

2. So cert is CERT = imei certificate = imei signature = imei key file.
If phone EFS/NV(place in phone where stored imei/cert) erased/wiped, phone modem will not work correctly!!

Do i have to write only cert to fix network, or write efs, qcn, sen and at last cert to make full repair?

3. What will hapend when i use wipe efs,nvm, and reset efs? Fo i have to write all, or cert have others inside?

4. will thi help for netowrk problems:
IF YOU CANNOT GET INTO GCF MODE (*must have root*)
1. ROOT THE PHONE WHICHEVER WAY YOU WANT TO HAVE ROOT ACCESS
2. DOWNLOAD APP CALLED "PHONE INFO" FOUND HERE OR PLAY STORE Phone INFO ?Samsung? 3.4.3 APK
3. CLICK MENU BAR IN TOP LEFT CORNER
4. CLICK OTHER TOOLS
5. CLICK SERVICE MODE (ROOT)
MUST HAVE ROOT FOR THIS TO WORK
AND FROM THERE YOU CAN ACCESS GCF