Please help me with K800i sim unlocking

[simox]

SeTool2 Lite doesn't display the box for using quick access patch, only the original bypass DB2020 security.

Probably you used the version 1.10 instead of 1.11

I have only been flashing the MAIN part of the firmware, not even having any FS firmware files, so how come my phone is still working?

Yes, it will work because you flashed only the MAIN, so the FS, GDFS, EROM remained untouched.

Is the EROM overwritten when flashing with MAIN firmware file?

No, it is untouched during "normal" flashing.

What's the difference between MAIN_GENERIC and MAIN_GENERIC_WI when talking of MAIN firmware files?

Actually there is no difference. WI - is the phone model identifier (WI = K800)

I've been flashing phone with R1JC002 firmware believing it to be the latest? Is it?

No, the latest version is R8BF003. Link: K800_RED52