I looked at the BBoA website picture of v4.3 motherboard and the FAT LADY is written on it and has a J102 jumper next to it, so it looks like v4.3 MBs had the FAT AGNUS installed.
Fat agnus just means it's not the A1000 agnus, which was also used in the german A2000. It only refers to the packaging size and the only functionality change was support for ranger memory @ c00000. Later changes like 1mb or 2mb chip ram and switchable 50/60fps can only be determined by the part number, they were all fat agnus.