Cert - These are certificates that are signed by Samsung's database. These are primarily used for IMEI numbers on phones. If the IMEI does not match the certificate hash with Samsung database then the phone will not be allowed cellular connection for sim card.
Cert files can be obtained by copying it from another phone and downloaded by places such as gsmhosting.
QCN - I think this is just another name for cert but in a different file format. I think it's for the older series of Samsung phones like qualcomm variants like the Samsung Galaxy S4 i9506-i9507.
NV data - Pretty much a partition or a bunch of stuff you can copy out of the phone that contains all the data such as Wi-Fi / Bluetooth MAC Address, Serial number of phone, IMEI number of phone and I'm not 100% sure probably the CERT and QCN as well.
Patch Certificate - An exploit that patches the modem firmware on phone used to allow Samsung phones to allow different IMEI numbers to work on the phone with invalid certificate match even. Only works currently on Android 6.0/6.0.1 (Marshmallow it seems). You can actually downgrade Android 7.0 (Nougat) Samsung phones back to Android 6.0/6.0.1(Marshmallow)
When you change an IMEI on a Samsung Galaxy S6 - S7 edge + you have to patch certificate after changing IMEI as the certificate will be identified as mismatch by the firmware installed on the phone. After it is patched it will accept the certificate and cellular signal will work as normal.
Do not WIPE EFS / QCN or NV Data (Backup all first if you really need to as a last resort), there is really no need to. I've never had the need to do so ever even when repairing lost IMEI on a phone.
And as always backup all the stuff like NV Data, EFS, QCN, CERT, SEC before performing any of these operations.
You are better off looking and asking for this information from gsmhosting.com as they specialise in this sort of stuff.
As I said above, patch certificate for changed IMEI only works on S6-S7edge+ with android 6.0.1 marshmallow.
Samsung Galaxy i9505 does not require it though and changing IMEI straight up usually just works.
The z3x box is also capable of doing FRP unlocks on Samsung phones too (one-click unlock on cheaper older models). Always try the other methods as shown on gsmhosting and youtube rootjunky and avoid flashing stuff onto phone as attempt to do it (downgrade is okay though in some cases). Also can do network unlocks on Samsung (also LG if you buy the activation for it).