hard to tell as the ps2 kext's have gotten highly fragmented over the years the kext names might be the same but they support totally different hardware. many coders have had there contributions and branches and usually it is to there benefit hardware wise. as a coder you can only thoroughly test the hardware you have on hand best. so basically using your example if the coder was in a country that uses 104 key keyboard he will most likely only code for that since thats what he has. if he had a 105 lets say then same.