I recently purchased two Samsung G5 phones from Amazon with the intent of ROM development on a downgraded version (the phone shipped with 5.0). I took one of the phones and successfully downgraded the device to an earlier 4x version without issue. It was only later when I attempted to do this on the second device that I ran into problems.
As it turns out, the same firmware I flashed on the first device does not seem to work with the second. After a bit of research I realized that the second device was of a different locale. Both devices, however, have the same model number. So this leaves me with the following questions:
What is it about different locales that may make firmware incompatible for same model devices? (Aside from carrier types: GSM, CDMA)
If a phone ships with a newer version, is it possible that downgrading may be impossible?
If not, what information, aside from the model number and region, is needed to select the proper firmware version for a deivce? (PDA,CSC, etc appear different across firmware versions)
Speaking to the third question listed above: I have attempted to flash countless 4x firmware images (for the correct model and region) only for the phone to get stuck at the Samsung splash screen.